xen-netfront: Fix mismatched rtnl_unlock

Fixes: f599c64f ("xen-netfront: Fix race between device setup and open")
Reported-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

BugLink: https://bugs.launchpad.net/bugs/1781413

(cherry picked from commit cb257783)
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Khaled Elmously <khalid.elmously@canonical.com>
Acked-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

drivers/net/xen-netfront.c

@@ -1821,7 +1821,7 @@ static int talk_to_netback(struct xenbus_device *dev,
 	err = xen_net_read_mac(dev, info->netdev->dev_addr);
 	if (err) {
 		xenbus_dev_fatal(dev, err, "parsing %s/mac", dev->nodename);
-		goto out;
+		goto out_unlocked;
 	}
 
 	rtnl_lock();
@@ -1936,6 +1936,7 @@ static int talk_to_netback(struct xenbus_device *dev,
 	xennet_destroy_queues(info);
  out:
 	rtnl_unlock();
+out_unlocked:
 	device_unregister(&dev->dev);
 	return err;
 }