in_addmulti
inm = in_addmulti(&tunnel->t_dst4, ifp0);
inm = in_addmulti(&sc->sc_syncpeer, ifp0);
sc->sc_inmulti = in_addmulti(&sc->sc_dst.in4, ifp0);
ia->ia_allhosts = in_addmulti(&addr, ifp);
struct in_multi *in_addmulti(const struct in_addr *, struct ifnet *);
if ((imm = in_addmulti(&addr, &sc->sc_if)) == NULL)
in_addmulti(&mreqn.imr_multiaddr, ifp)) == NULL) {