net/mlx5: Lag, support single FDB only on 2 ports

E-Switch currently doesn't support more than 2 E-Switch managers
being aggregated under a single hardware lag. Have specific checks
to disallow creating lag when the code doesn't support it.
Signed-off-by: NMark Bloch <mbloch@nvidia.com>
Reviewed-by: NMaor Gottlieb <maorg@nvidia.com>
Signed-off-by: NSaeed Mahameed <saeedm@nvidia.com>

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

@@ -458,6 +458,7 @@ static int mlx5_deactivate_lag(struct mlx5_lag *ldev)
 	return 0;
 }
 
+#define MLX5_LAG_OFFLOADS_SUPPORTED_PORTS 2
 static bool mlx5_lag_check_prereq(struct mlx5_lag *ldev)
 {
 #ifdef CONFIG_MLX5_ESWITCH
@@ -470,6 +471,9 @@ static bool mlx5_lag_check_prereq(struct mlx5_lag *ldev)
 #ifdef CONFIG_MLX5_ESWITCH
 	mode = mlx5_eswitch_mode(ldev->pf[MLX5_LAG_P1].dev);
 
+	if (mode == MLX5_ESWITCH_OFFLOADS && ldev->ports != MLX5_LAG_OFFLOADS_SUPPORTED_PORTS)
+		return false;
+
 	return (mode == MLX5_ESWITCH_NONE || mode == MLX5_ESWITCH_OFFLOADS) &&
 		(mlx5_eswitch_mode(ldev->pf[MLX5_LAG_P1].dev) ==
 		 mlx5_eswitch_mode(ldev->pf[MLX5_LAG_P2].dev));