net/mlx5: fix VLAN inner type matching on DR/DV

net/mlx5: fix VLAN inner type matching on DR/DV

The rte_flow_item_vlan has the inner_type, which is missing on
DR/DV flow engine.

By adding this support, the example testpmd commands could be:

 - matching all vlan traffic with id 2:

 testpmd> flow create 0 ingress pattern eth / vlan vid is 2 / end
          actions queue index 2 / end

 - matching all ipv4 traffic in vlan with id 2:

 testpmd> flow create 0 ingress pattern eth / vlan vid is 2
          inner_type is 0x0800 / end actions queue index 2 / end

Fixes: fc2c498ccb94 ("net/mlx5: add Direct Verbs translate items")
Cc: stable@dpdk.org
Signed-off-by: Xiaoyu Min <jackmin@mellanox.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>