net/sched: support per action hw stats

There are currently two mechanisms for populating hardware stats:
1. Using flow_offload api to query the flow's statistics.
   The api assumes that the same stats values apply to all
   the flow's actions.
   This assumption breaks when action drops or jumps over following
   actions.
2. Using hw_action api to query specific action stats via a driver
   callback method. This api assures the correct action stats for
   the offloaded action, however, it does not apply to the rest of the
   actions in the flow's actions array.

Extend the flow_offload stats callback to indicate that a per action
stats update is required.
Use the existing flow_offload_action api to query the action's hw stats.
In addition, currently the tc action stats utility only updates hw actions.
Reuse the existing action stats cb infrastructure to query any action
stats.

Signed-off-by: Oz Shlomo <ozsh@nvidia.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Reviewed-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>