net/mlx5e: Add qos capability check

Make sure firmware supports qos before exposing the DCB API.
Signed-off-by: Huy Nguyen <huyn@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlx5/core/en_main.c

@@ -3549,6 +3549,7 @@ static void mlx5e_build_nic_netdev(struct net_device *netdev)
 	if (MLX5_CAP_GEN(mdev, vport_group_manager)) {
 		netdev->netdev_ops = &mlx5e_netdev_ops_sriov;
 #ifdef CONFIG_MLX5_CORE_EN_DCB
+		if (MLX5_CAP_GEN(mdev, qos))
 			netdev->dcbnl_ops = &mlx5e_dcbnl_ops;
 #endif
 	} else {