TUN_OPEN
if ((tp->tun_flags & (TUN_OPEN | TUN_DYING)) != 0) {
tp->tun_flags |= TUN_OPEN;
tp->tun_flags &= ~TUN_OPEN;
#define TUN_READY (TUN_OPEN | TUN_INITED)
if (tp->tun_flags & TUN_OPEN)