ifwithindex
extern struct interface *ifwithindex(ulong_t, boolean_t);
if ((ifp = ifwithindex(ifindex, _B_TRUE)) != NULL) {
ifp = ifwithindex(sdl->sdl_index, _B_TRUE);
ifp = ifwithindex(m.ifm.ifm_index,
ifp = ifwithindex(m.r.rtm.rtm_index, 1);