in_addmulti
lmsg->u.ms_resultp = in_addmulti(&addr, ifp);
in_addmulti(&addr, ifp);
struct in_multi *in_addmulti (struct in_addr *, struct ifnet *);
imo->imo_membership[0] = in_addmulti(&addr, &sc->sc_if);
in_addmulti(&mreqn.imr_multiaddr, ifp)) == NULL) {