ifa_alloc
ifa = ifa_alloc(ifasize, M_WAITOK);
struct ifaddr * ifa_alloc(size_t size, int flags);
ifa = ifa_alloc(sizeof(struct in_ifaddr), M_WAITOK);
ia = (struct in6_ifaddr *)ifa_alloc(sizeof(*ia), M_NOWAIT);
ifa = ifa_alloc(sizeof(struct in6_ifaddr), M_NOWAIT);