cls_api: add translator to flow_action representation

This patch implements a new function to translate from native TC action
to the new flow_action representation. Moreover, this patch also updates
cls_flower to use this new function.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>