net/mlx5e: Disable loopback self-test on multi-PF netdev

In Multi-PF (Socket Direct) configurations, when a loopback packet is
sent through one of the secondary devices, it will always be received
on the primary device. This causes the loopback layer to fail in
identifying the loopback packet as the devices are different.

To avoid false test failures, disable the loopback self-test in
Multi-PF configurations.

Fixes: ed29705 ("net/mlx5: Enable SD feature")
Signed-off-by: Carolina Jubran <cjubran@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/20241107183527.676877-8-tariqt@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: cjubran

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

@@ -36,6 +36,7 @@
 #include "en.h"
 #include "en/port.h"
 #include "eswitch.h"
+#include "lib/mlx5.h"
 
 static int mlx5e_test_health_info(struct mlx5e_priv *priv)
 {
@@ -247,6 +248,9 @@ static int mlx5e_cond_loopback(struct mlx5e_priv *priv)
 	if (is_mdev_switchdev_mode(priv->mdev))
 		return -EOPNOTSUPP;
 
+	if (mlx5_get_sd(priv->mdev))
+		return -EOPNOTSUPP;
+
 	return 0;
 }