tun: move the call to tun_set_real_num_queues

Call tun_set_real_num_queues() after the increment of tun->numqueues
since the former depends on it. Otherwise, the number of queues is not
correctly accounted for, which results to warnings similar to:
"vnet0 selects TX queue 11, but real number of TX queues is 11".

Fixes: 0b7959b6 ("tun: publish tfile after it's fully initialized")
Reported-and-tested-by: George Amanakis <gamanakis@gmail.com>
Signed-off-by: George Amanakis <gamanakis@gmail.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/tun.c

@@ -866,8 +866,6 @@ static int tun_attach(struct tun_struct *tun, struct file *file,
 	if (rtnl_dereference(tun->xdp_prog))
 		sock_set_flag(&tfile->sk, SOCK_XDP);
 
-	tun_set_real_num_queues(tun);
-
 	/* device is allowed to go away first, so no need to hold extra
 	 * refcnt.
 	 */
@@ -879,6 +877,7 @@ static int tun_attach(struct tun_struct *tun, struct file *file,
 	rcu_assign_pointer(tfile->tun, tun);
 	rcu_assign_pointer(tun->tfiles[tun->numqueues], tfile);
 	tun->numqueues++;
+	tun_set_real_num_queues(tun);
 out:
 	return err;
 }