net/mlx5e: Don't support phys switch id if not in switchdev mode

stable inclusion
from linux-4.19.145
commit 044be307e550b4532960eadabfb6942de96751f0

--------------------------------

Support for phys switch id ndo added for representors and if
we do not have representors there is no need to support it.
Since each port return different switch id supporting this
block support for creating bond over PFs and attaching to bridge
in legacy mode.

This bug doesn't exist upstream as the code got refactored and the
netdev api is totally different.

Fixes: cb67b832 ("net/mlx5e: Introduce SRIOV VF representors")
Signed-off-by: NRoi Dayan <roid@mellanox.com>
Signed-off-by: NSaeed Mahameed <saeedm@mellanox.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>
Signed-off-by: NAichun Li <liaichun@huawei.com>
Reviewed-by: Nwangxiaopeng <wangxiaopeng7@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

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

@@ -198,7 +198,7 @@ int mlx5e_attr_get(struct net_device *dev, struct switchdev_attr *attr)
 	struct mlx5_eswitch_rep *rep = rpriv->rep;
 	struct mlx5_eswitch *esw = priv->mdev->priv.eswitch;
 
-	if (esw->mode == SRIOV_NONE)
+	if (esw->mode != SRIOV_OFFLOADS)
 		return -EOPNOTSUPP;
 
 	switch (attr->id) {