ospf: BFD down not tearing down OSPF adjacency for point-to-point network

ospf: BFD down not tearing down OSPF adjacency for point-to-point network

Root Cause:
Lookup for the point-to-point neighbor was failing because the neighbor
lookup was based on neighbor interface IP address. But, for point-to-point
neighbor the key is router-id for lookup. Lookup failure was causing the
BFD updates from PTM to get dropped.

Fix:
Added walk of the neighbor list if the network type is point-to-point to
find the appropriate neighbor. The match is based on source IP address of
the neighbor since that’s the address registered with BFD for monitoring.

Ticket: CM-20411
Signed-off-by: Radhika Mahankali <radhika@cumulusnetworks.com>