bgpd: touch nexthop handling code

bgp_nexthop_lookup_ipv6(): declare variables where they are actually
used, drop no-op initialization (the field is already 0)
bgp_nexthop_lookup(): ditto
bgp_nexthop_check_ebgp(): rename to bgp_nexthop_onlink()
bgp_nexthop_cache_changed(): rename to bgp_nexthop_cache_different()
3 files changed