net/mlx5: Add core support for vlan push/pop steering action

Newer NICs (ConnectX-5 and onward) can apply vlan pop or push as an
action taking place during flow steering. Add the core bits for that.

Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Reviewed-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>