net/mlx4_en: User prio mapping gets corrupted when changing number of channels

When using ethtool set_channels, mlx4_en_setup_tc is always called, even
when it was not configured. Fixed code to call mlx4_en_setup_tc() only
if needed.
Signed-off-by: Ido Shamay <idos@mellanox.com>
Signed-off-by: Amir Vadai <amirv@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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

@@ -1151,6 +1151,7 @@ static int mlx4_en_set_channels(struct net_device *dev,
 	netif_set_real_num_tx_queues(dev, priv->tx_ring_num);
 	netif_set_real_num_rx_queues(dev, priv->rx_ring_num);
 
+	if (dev->num_tc)
 		mlx4_en_setup_tc(dev, MLX4_EN_NUM_UP);
 
 	en_warn(priv, "Using %d TX rings\n", priv->tx_ring_num);