in_addmulti
in_addmulti(&addr, sc->sc_sync_ifp)) == NULL) {
ia->ia_allhosts = in_addmulti(&addr, ifp);
struct in_multi *in_addmulti(struct in_addr *, struct ifnet *);
if ((imm = in_addmulti(&addr, &sc->sc_if)) == NULL)
imo->imo_membership[i] = in_addmulti(&ia, ifp);