illif_mcast_v2
uint16_t illif_mcast_v2; /* [igmp|mld]_slowtimo */
#define illif_mcast_v2 ill_if_s.illif_mcast_v2
if (ifp->illif_mcast_v1 == 0 && ifp->illif_mcast_v2 == 0)
atomic_dec_16(&ifp->illif_mcast_v2);
atomic_inc_16(&ill->ill_ifptr->illif_mcast_v2);