net/mlx5: E-Switch, Allow fine tuning of eswitch vport push/pop vlan

The HW can be programmed to push vlan, pop vlan or both.

A factorization step towards using the push/pop capabilties in the
eswitch offloads mode. This patch doesn't add new functionality.

Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>