bgpd: update topotests for role mismatch

bgpd: update topotests for role mismatch

In topotests, we also want to check for role mismatch cases. However, if
we are testing the sender of a role mismatch notification, sometimes it
can have non-deterministic behavior (probably due to a configuration
change). Thus, there is an assumption that the recipient of
notifications will more consistently display the reason why the session
was terminated in the first place.

Signed-off-by: Eugene Bogomazov <eb@qrator.net>