nfp: flower: restructure flow-key for gre+vlan combination

Swap around the GRE and VLAN parts in the flow-key offloaded by
the driver to fit in with other tunnel types and the firmware.
Without this change used cases with GRE+VLAN on the outer header
does not get offloaded as the flow-key mismatches what the
firmware expect.

Fixes: 0d630f58 ("nfp: flower: add support to offload QinQ match")
Fixes: 5a2b9304 ("nfp: flower-ct: compile match sections of flow_payload")
Signed-off-by: Etienne van der Linde <etienne.vanderlinde@corigine.com>
Signed-off-by: Louis Peens <louis.peens@corigine.com>
Signed-off-by: Yinjun Zhang <yinjun.zhang@corigine.com>
Signed-off-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>