mlx4: protect mlx4_en_start_port in mlx4_en_restart with rtnl_lock

mlx4_en_start_port requires rtnl_lock to be held.

Cc: Eugenia Emantayev <eugenia@mellanox.com>
Cc: Yishai Hadas <yishaih@mellanox.com>
Signed-off-by: NHannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlx4/en_netdev.c

@@ -1856,6 +1856,7 @@ static void mlx4_en_restart(struct work_struct *work)
 
 	en_dbg(DRV, priv, "Watchdog task called for port %d\n", priv->port);
 
+	rtnl_lock();
 	mutex_lock(&mdev->state_lock);
 	if (priv->port_up) {
 		mlx4_en_stop_port(dev, 1);
@@ -1863,6 +1864,7 @@ static void mlx4_en_restart(struct work_struct *work)
 			en_err(priv, "Failed restarting port %d\n", priv->port);
 	}
 	mutex_unlock(&mdev->state_lock);
+	rtnl_unlock();
 }
 
 static void mlx4_en_clear_stats(struct net_device *dev)