net/mlx5: Prevent flow steering mode changes in switchdev mode

Changing flow steering modes is not allowed when eswitch is in switchdev
mode. This fix ensures that any steering mode change, including to
firmware steering, is correctly blocked while eswitch mode is switchdev.

Fixes: e890acd ("net/mlx5: Add devlink flow_steering_mode parameter")
Signed-off-by: Moshe Shemesh <moshe@nvidia.com>
Signed-off-by: Mark Bloch <mbloch@nvidia.com>
Link: https://patch.msgid.link/20250825143435.598584-9-mbloch@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: mosheshemesh2

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

@@ -3734,6 +3734,13 @@ static int mlx5_fs_mode_validate(struct devlink *devlink, u32 id,
 	char *value = val.vstr;
 	u8 eswitch_mode;
 
+	eswitch_mode = mlx5_eswitch_mode(dev);
+	if (eswitch_mode == MLX5_ESWITCH_OFFLOADS) {
+		NL_SET_ERR_MSG_FMT_MOD(extack,
+				       "Changing fs mode is not supported when eswitch offloads enabled.");
+		return -EOPNOTSUPP;
+	}
+
 	if (!strcmp(value, "dmfs"))
 		return 0;
 
@@ -3759,14 +3766,6 @@ static int mlx5_fs_mode_validate(struct devlink *devlink, u32 id,
 		return -EINVAL;
 	}
 
-	eswitch_mode = mlx5_eswitch_mode(dev);
-	if (eswitch_mode == MLX5_ESWITCH_OFFLOADS) {
-		NL_SET_ERR_MSG_FMT_MOD(extack,
-				       "Moving to %s is not supported when eswitch offloads enabled.",
-				       value);
-		return -EOPNOTSUPP;
-	}
-
 	return 0;
 }