nfp: flower: add support to offload QinQ match

When both the driver and the firmware supports QinQ the flow key
structure that is send to the firmware is updated as the old
method of matching on VLAN did not allow for space to add another
VLAN tag. VLAN flows can now also match on the tpid field, not
constrained to just 0x8100 as before.

Signed-off-by: Louis Peens <louis.peens@netronome.com>
Signed-off-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>