ethdev: fix default VLAN TCI mask in flow API

ethdev: fix default VLAN TCI mask in flow API

VLAN TCI is a 16-bit field broken down as PCP (3b), DEI (1b) and VID (12b).

The default mask used by PMDs for the VLAN pattern when one isn't provided
by the application comprises the entire TCI, which is problematic because
most devices only support VID matching.

This forces applications to always provide a mask limited to the VID part
in order to successfully apply a flow rule with a VLAN pattern item.
Moreover, applications rarely want to match PCP and DEI intentionally.

Given the above and since VID is what is commonly referred to when talking
about VLAN, this commit excludes PCP and DEI from the default mask.

Fixes: 6de5c0f1302c ("ethdev: define default item masks in flow API")

Signed-off-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>
Acked-by: Andrew Rybchenko <arybchenko@solarflare.com>