Resolve neighbors using longest prefix match. Although interface ranges
should not generally collide, it may happen for unnumbered links.

Thanks to Kenth Eriksson for the bugreport.

This is merely a const propagation. There was no problem in there.

Modify protocols to use preferred address change notification instead on
depending on hard-reset of interfaces in that case, and remove hard-reset
in that case. This avoids issue when e.g. IPv6 protocol restarts
interface when IPv4 preferred address changed (as hard-reset is
unavoidable and common for whole iface).

The patch also fixes a bug when removing last address does not send
preferred address change notification.

Simplify neighbor cache code, fix several minor bugs, and improve
handling of ONLINK flag.

Also redesign preferred address selection and update protocols to use
appropriate preferred address.

Based on a previous work by Jan Maria Matejka.

Add basic VRF (virtual routing and forwarding) support. Protocols can be
associated with VRFs, such protocols will be restricted to interfaces
assigned to the VRF (as reported by Linux kernel) and will use sockets
bound to the VRF. E.g., different multihop BGP instances can use diffent
kernel routing tables to handle BGP TCP connections.

The VRF support is preliminary, currently there are several limitations:

- Recent Linux kernels (4.11) do not handle correctly sockets bound
to interaces that are part of VRF, so most protocols other than multihop
BGP do not work. This will be fixed by future kernel versions.

- Neighbor cache ignores VRFs. Breaks config with the same prefix on
local interfaces in different VRFs. Not much problem as single hop
protocols do not work anyways.

- Olock code ignores VRFs. Breaks config with multiple BGP peers with the
same IP address in different VRFs.

- Incoming BGP connections are not dispatched according to VRFs.
Breaks config with multiple BGP peers with the same IP address in
different VRFs. Perhaps we would need some kernel API to read VRF of
incoming connection? Or probably use multiple listening sockets in
int-new branch.

- We should handle master VRF interface up/down events and perhaps
disable associated protocols when VRF goes down. Or at least disable
associated interfaces.

- Also we should check if the master iface is really VRF iface and
not some other kind of master iface.

- BFD session request dispatch should be aware of VRFs.

- Perhaps kernel protocol should read default kernel table ID from VRF
iface so it is not necessary to configure it.

- Perhaps we should have per-VRF default table.

 - Unit Testing Framework (BirdTest)
 - Integration of BirdTest into the BIRD build system
 - Tests for several BIRD modules

 Based on squashed Pavel Tvrdik's int-test branch, updated for
 current int-new branch.

Use net_addr for interface address prefixes, support net_addr in
configuration parser.

Router ID could be automatically determined based of subset of
ifaces/addresses specified by 'router id from' option. The patch also
does some minor changes related to router ID reconfiguration.

Thanks to Alexander V. Chernikov for most of the work.

Allows using NEF_STICKY neighbors with link-local addresses. This is
used for static route nexthops, they can be specified like fe80::1%eth0
.

Thanks Matthias Schiffer for the bugreport and the original patch.

Mainly changes IA_UNNUMBERED to IA_PEER and adds IA_HOST. Also do not
show broadcast addr in show interfaces. Nobody cares for that.

Also changes some symbol names (IFF_ADMIN_DOWN -> IFF_SHUTDOWN,
IFF_LINK_UP -> IFF_ADMIN_UP).

When device protocol goes down, interfaces should be flushed
asynchronously (in the same way like routes from protocols are flushed),
when protocol goes to DOWN/HUNGRY.

This fixes the problem with static routes staying in kernel routing
table after BIRD shutdown.

- BSD kernel syncer is now self-conscious and can learn alien routes
- important bugfix in BSD kernel syncer (crash after protocol restart)
- many minor changes and bugfixes in kernel syncers and neighbor cache
- direct protocol does not generate host and link local routes
- min_scope check is removed, all routes have SCOPE_UNIVERSE by default
- also fixes some remaining compiler warnings

Finally, it is working.

Allows to add more interface patterns to one common 'options'
section like:

interface "eth3", "eth4" { options common to eth3 and eth4 };

Also removes undocumented and unnecessary ability to specify
more interface patterns with different 'options' sections:

interface "eth3" { options ... }, "eth4" { options ... };

(1) obsolete and (2) replaced by the progdoc.

neighbor->scope now contains proper address scope which is zero (SCOPE_HOST)
for local addresses, higher (SCOPE_LINK, ..., SCOPE_UNIVERSE) for remote ones.

Introduced neigh_connected_to() to serve the same purpose efficiently.

address, not per interface (hence it's ifa->flags & IA_UNNUMBERED) and
should be set reliably. IF_MULTIACCESS should be fixed now, but it isn't
wise to rely on it on interfaces configured with /30 prefix.

Manual disable/enable/restart/shutdown/reconfiguration of protocols
no longer hangs on loops in neighbor lists :)

show protocols (incomplete).

   o  Parsing of interface patterns moved to generic code,
      introduced this_ipatt which works similarly to this_iface.
   o  Interface patterns now support selection by both interface
      names and primary IP addresses.
   o  Proto `direct' updated.
   o  RIP updated as well, it also seems the memory corruption
      bug there is gone.

addresses per interface (needed for example for IPv6 support).

Visible changes:

o  struct iface now contains a list of all interface addresses (represented
   by struct ifa), iface->addr points to the primary address (if any).
o  Interface has IF_UP set iff it's up and it has a primary address.
o  IF_UP is now independent on IF_IGNORED (i.e., you need to test IF_IGNORED
   in the protocols; I've added this, but please check).
o  The if_notify_change hook has been simplified (only one interface pointer
   etc.).
o  Introduced a ifa_notify_change hook. (For now, only the Direct protocol
   does use it -- it's wise to just listen to device routes in all other
   protocols.)
o  Removed IF_CHANGE_FLAGS notifier flag (it was meaningless anyway).
o  Updated all the code except netlink (I'll look at it tomorrow) to match
   the new semantics (please look at your code to ensure I did it right).

Things to fix:

o  Netlink.
o  Make krt-iface interpret "eth0:1"-type aliases as secondary addresses.

o  Introduced if_find_by_index()
o  Recognizing two types of interface updates: full update (starting with
   if_start_update(), ending with if_end_update(), guaranteed to see
   all existing interfaces) and a partial update (only if_update(),
   usually due to asynchronous interface notifications).