xen-netfront: fix locking in connect error path

If no queues could be created when connecting to the backend, one of the
error paths would deadlock.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/xen-netfront.c

@@ -2001,7 +2001,7 @@ abort_transaction_no_dev_fatal:
 	info->queues = NULL;
 	rtnl_lock();
 	netif_set_real_num_tx_queues(info->netdev, 0);
-	rtnl_lock();
+	rtnl_unlock();
  out:
 	return err;
 }