Comment 1 for bug 1574169

I think we missed one scenario in the previous fix.

Add operation is enqueued to DB, unsubscribe for the
instance is received, membership manager API to
unregister table is called, membership managers starts
leave and part of the table is walked but membership
manager has not yet removed IPeerRib, add operation
is processed and path gets added.

Fix could be to invalidate the subscribe gen id before
or when leave starts.