This function is a part of Readline interface for a long time
(with a different type).

Thanks to Aleksey Berezin for the bugreport.

Thanks to MrBr for the bugreport.

Also significant core protocol state changes needed for that,
global graceful restart recovery state and kernel proto support
for recovery.

The old static route was not removed when the nexthop changed and the
new one was not viable (no neighbor).

Thanks to Pierluigi Rolando for the original patch.

Thanks to Pierluigi Rolando and others for the bugreport.

Thanks to Pierluigi Rolando for the bugreport.

Thanks to Ondrej Caletka for the bugreport.

I/O:
 - BSD: specify src addr on IP sockets by IP_HDRINCL
 - BSD: specify src addr on UDP sockets by IP_SENDSRCADDR
 - Linux: specify src addr on IP/UDP sockets by IP_PKTINFO
 - IPv6: specify src addr on IP/UDP sockets by IPV6_PKTINFO
 - Alternative SKF_BIND flag for binding to IP address
 - Allows IP/UDP sockets without tx_hook, on these
   sockets a packet is discarded when TX queue is full
 - Use consistently SOL_ for socket layer values.

OSPF:
 - Packet src addr is always explicitly set
 - Support for secondary addresses in BSD
 - Dynamic RX/TX buffers
 - Fixes some minor buffer overruns
 - Interface option 'tx length'
 - Names for vlink pseudoifaces (vlinkX)
 - Vlinks use separate socket for TX
 - Vlinks do not use fixed associated iface
 - Fixes TTL for direct unicast packets
 - Fixes DONTROUTE for OSPF sockets
 - Use ifa->ifname instead of ifa->iface->name

Fixes some bugs and uses generic hash implementation.

Thanks to Alexander V. Chernikov for the original patch.