bgp: consider adding plumbing for interface association of peer #619
Description
Currently there is no plumbing that associates a BGP peer with a network interface. This means for IPv6 peering, that we must prefer the GUA next-hop in circumstances where the peer sends us both GUA + Link-local next-hops, because we are unable to tie the link-local address to its scope.
We should consider adding plumbing for interface association of a peer, that way we have the ability to make use of Link-local next-hops instead of always relying on the GUA address having a connected route.
Somewhat related: #562