bgpd: Address LL peer not NHT when receiving connection attempt

bgpd: Address LL peer not NHT when receiving connection attempt

The new LL code in:
8761cd6ddb5437767625f58c8e9cc3ccda7887ab

Introduced the idea of the bgp unnumbered peers using interface up/down
events to track the bgp peers nexthop.  This code was not properly
working when a connection was received from a peer in some circumstances.

Effectively the connection from a peer was immediately skipping state transitions
and FRR was never properly tracking the peers nexthop.  When we receive the
connection attempt, let's track the nexthop now.

Signed-off-by: Donald Sharp <sharpd@nvidia.com>