bgpd: Fix deterministic-med check for stale paths

bgpd: Fix deterministic-med check for stale paths

When performing deterministic MED processing, ensure that the peer
status is not checked when we encounter a stale path. Otherwise, this
path will be skipped from the DMED consideration leading to it potentially
not being installed.

Test scenario: Consider a prefix with 2 (multi)paths. The peer that
announces the path with the winning DMED undergoes a graceful-restart.
Before it comes back up, the other path goes away. Prior to the fix, a
third router that receives both these paths would have ended up not
having any path installed to the prefix after the above events.

Signed-off-by: Vivek Venkatraman <vivek@nvidia.com>
For internal use:
Ticket: CM-32032
Testing done: Multiple manual testing