net/mlx5: fix match on empty VLAN item in DV mode

net/mlx5: fix match on empty VLAN item in DV mode

In existing implementation, using wild card VLAN item is not allowed.
A VLAN item in flow pattern must include VLAN ID (vid) value.
This obligation contradict the flow API specification [1].

This patch updates the VLAN item validation and translation, to allow
wild card VLAN item, without VLAN ID value.
User guide and release notes are updated accordingly.

[1]
commit 40513808b165 ("doc: refine ethernet and VLAN flow rule items")

Fixes: 00f75a40576b ("net/mlx5: fix VLAN match for DV mode")
Cc: stable@dpdk.org
Signed-off-by: Dekel Peled <dekelp@mellanox.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>