bgpd: Only update peer connection information when needed

bgpd: Only update peer connection information when needed

Currently bgp is repeatedly grabbing peer connection information.
This is a bit overkill.  There are two situations:

a) Opening a connection to the peer
   In this case, we know the remote port/address a priori and can get
   the local information by just asking the OS.
b) Peer opening a connection to us.
   In this case, we know the local port/address a priori and can get
   the remote information by just asking the OS.

Modify the code to just grab this data at the appropriate time.

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