net/mlx5: split sample flow into two sub-flows

net/mlx5: split sample flow into two sub-flows

The flow with sample action will be split into two sub flows:
the prefix sub flow with the all actions preceding the sample
action and sample action itself, and the suffix sub flow with
the actions following the sample action.

The original items remain in the prefix sub flow, add the
implicit tag action with unique id to set in metadata register,
and suffix sub flow uses the tag item to match with that unique id.

The flow split as below:

Original flow: items / actions pre / sample / actions sfx ->
    prefix sub flow -
            items / actions pre / set_tag action / sample
    suffix sub flow -
            tag_item / actions sfx

Signed-off-by: Jiawei Wang <jiaweiw@nvidia.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>