Also fixes some more failed asserts due to add_tail().

Support for dynamically spawning BGP protocols for incoming connections.
Use 'neighbor range' to specify range of valid neighbor addresses, then
incoming connections from these addresses spawn new BGP instances.

The glibc's generic parser is slow due to its versatility. Specialized
parsers for base-10 and base-16 are much faster and we don't use other
bases.

... and consted some declarations.

This should be revised, there are still ugly things in the filter API.

The old hash table had fixed size, which makes it slow for config files
with large number of symbols and symbol lookups. The new one is growing
according to needs.

When shift count >= width of type the behavior is undefined.

Allow to define static roa/flow routes without dest.

From now on, protocol static accepts VPN4 and VPN6 addressess.
With some concerns about VPN6 Route Distinguishers, I finally chose
to have the same format as for VPN4 (where it is defined by RFC 4364).

Thanks to Ondrej Zajicek for code.

Symbol lookup by cf_find_symbol() not only did the lookup but also added
new void symbols allocated from cfg_mem linpool, which gets broken when
lookups are done outside of config parsing, which may lead to crashes
during reconfiguration.

The patch separates lookup-only cf_find_symbol() and config-modifying
cf_get_symbol(), while the later is called only during parsing. Also
new_config and cfg_mem global variables are NULLed outside of parsing.

New data types net_addr and variants (in lib/net.h) describing
network addresses (prefix/pxlen). Modifications of FIB structures
to handle these data types and changing everything to use these
data types instead of prefix/pxlen pairs where possible.

The commit is WiP, some protocols are not yet updated (BGP, Kernel),
and the code contains some temporary scaffolding.

Comments are welcome.

And move the constant to conf.h header.

Thanks to Alexander Chernikov for the patch.

Thanks to Michael Fincham for the bugreport.

Thanks to MrBr for the bugreport.

Also fixes some minor bugs in include.

Thanks Kelly Cochran for suggestion and draft patch.

 - ROA tables, which are used as a basic part for RPKI.
 - Commands for examining and modifying ROA tables.
 - Filter operators based on ROA tables consistent with RFC 6483.