netdev-tc-offloads: Support match on priority tags

netdev-tc-offloads: Support match on priority tags

The logic by which a TC rule has a VLAN match is by the VLAN TCI field,
either the VID, PCP or CFI are non-zero. For priority-tag packets
there is a VLAN tag header with a zero VLAN TCI. Match on existence of
VLAN header (TPID) regardless of TCI matching.

Signed-off-by: Eli Britstein <elibr@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Simon Horman <simon.horman@netronome.com>