net/mlx5e: Fix HW MTU settings

Previously we configured HW MTU to be netdev->mtu, actually we
need to configure netdev->mtu + (ETH_HLEN + VLAN_HLEN + ETH_FCS_LEN).

Also, query MTU can not fail, hence make the relevant helper a
void functionm, add mlx5e_set_dev_port_mtu, helper function to
handle MTU setting.

Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/infiniband/hw/mlx5/main.c b/drivers/infiniband/hw/mlx5/main.c
index d4dea86..79dadd6 100644
--- a/drivers/infiniband/hw/mlx5/main.c
+++ b/drivers/infiniband/hw/mlx5/main.c
@@ -446,15 +446,11 @@
 	if (err)
 		goto out;
 
-	err = mlx5_query_port_max_mtu(mdev, &max_mtu, port);
-	if (err)
-		goto out;
+	mlx5_query_port_max_mtu(mdev, &max_mtu, port);
 
 	props->max_mtu = mlx5_mtu_to_ib_mtu(max_mtu);
 
-	err = mlx5_query_port_oper_mtu(mdev, &oper_mtu, port);
-	if (err)
-		goto out;
+	mlx5_query_port_oper_mtu(mdev, &oper_mtu, port);
 
 	props->active_mtu = mlx5_mtu_to_ib_mtu(oper_mtu);