bfdd: Handling local and remote admin-down

bfdd: Handling local and remote admin-down

Scenarios where this code change is required:

1. BFD is un-configured from BGP at remote end.

Neighbour BFD sends ADMIN_DOWN state, but BFD on local side will send
DOWN to BGP, resulting in BGP session DOWN.
Removing BFD session administratively shouldn't bring DOWN BGP session
at local or remote.

2. BFD is un-configured from BGP or shutdown locally.

BFD will send state DOWN to BGP resulting in BGP session DOWN.
(This is akin to saying do not use BFD for BGP)
Removing BFD session administratively shouldn't bring DOWN BGP session at
local or remote.

Signed-off-by: Sayed Mohd Saquib sayed.saquib@broadcom.com