nd6_need_cache
if (nd6_need_cache(ifp) && (ifp->if_flags & IFF_MULTICAST) == 0)
if (nd6_need_cache(ifp) == 0 && (rt->rt_flags & RTF_HOST) == 0) {
if (req == RTM_RESOLVE && nd6_need_cache(ifp) == 0) {
int nd6_need_cache(struct ifnet *);