Don't remove ADB entry from LRU before trying to expire it

Don't remove ADB entry from LRU before trying to expire it

There was a code flow error that would remove the expired ADB entry from
the LRU list and then a check in the expire_entry() would cause
assertion error because it expect the ADB entry to be linked.

Additionally, the expire mechanism would loop for cases when we would
held only a read rwlock; in such case we need to upgrade the lock and
try again, not just try again.