TUN_OPEN
KASSERTMSG(!tp || (tp->tun_flags & (TUN_INITED|TUN_OPEN)) == TUN_OPEN,
if (tp->tun_flags & TUN_OPEN) {
if (tp->tun_flags & TUN_OPEN) {
tp->tun_flags |= TUN_OPEN;
tp->tun_flags &= ~TUN_OPEN;
#define TUN_READY (TUN_OPEN | TUN_INITED | TUN_IASET)