ethdev: add VLAN attributes to ethernet and VLAN items

ethdev: add VLAN attributes to ethernet and VLAN items

This patch implements the change proposes in RFC [1], adding dedicated
fields to ETH and VLAN items structs, to clearly define the required
characteristic of a packet, and enable precise match criteria.
Documentation is updated accordingly.

[1] https://mails.dpdk.org/archives/dev/2020-August/177536.html

Signed-off-by: Dekel Peled <dekelp@nvidia.com>
Acked-by: Matan Azrad <matan@nvidia.com>
Acked-by: Ori Kam <orika@nvidia.com>