nfp: flower: support hw offload for ct nat action

support ct nat action when pre_ct merge with post_ct
and nft. at the same time, add the extra checksum action
and hardware stats for nft to meet the action check when
do nat.

Signed-off-by: Hui Zhou <hui.zhou@corigine.com>
Reviewed-by: Louis Peens <louis.peens@corigine.com>
Signed-off-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>