The tip hash is only used when we are dealing with
evpn. In bgp_nexthop_self we are doing a memset
irrelevant of whether we will ever find data. Yes
hash_lookup will return pretty quickly.
Modify the code to avoid doing a memset in the case
where the tip hash is empty as that we know we'll
never find anything. With full BGP feeds this
small memset does take some time.