TUN_TRANSIENT
if ((tp->tun_flags & TUN_TRANSIENT) != 0) {
tp->tun_flags |= TUN_TRANSIENT;
tp->tun_flags &= ~TUN_TRANSIENT;
*(int *)data = (tp->tun_flags & TUN_TRANSIENT) != 0;
MPASS((tp->tun_flags & (TUN_DYING | TUN_TRANSIENT)) != TUN_DYING);
if ((tp->tun_flags & TUN_TRANSIENT) != 0) {