tun: remove unnecessary memory barrier

Replace set_current_state with __set_current_state since no memory
barrier is needed at this point.
Signed-off-by: Timur Celik <mail@timurcelik.de>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/tun.c

@@ -2185,7 +2185,7 @@ static void *tun_ring_recv(struct tun_file *tfile, int noblock, int *err)
 		schedule();
 	}
 
-	set_current_state(TASK_RUNNING);
+	__set_current_state(TASK_RUNNING);
 	remove_wait_queue(&tfile->wq.wait, &wait);
 
 out: