net/mlx4: support flow API RSS action

net/mlx4: support flow API RSS action

This commit adds support for the flow API RSS action with the following
limitations:

 - Only supported when isolated mode is enabled.
 - The number of queues specified by the action (rte_flow_action_rss.num)
   must be a power of two.
 - Each queue index can be specified at most once in the configuration
   (rte_flow_action_rss.queue[]).
 - Because a queue can be associated with a single RSS context, it cannot
   be targeted by multiple RSS actions simultaneously.

Signed-off-by: Vasily Philipov <vasilyf@mellanox.com>
Acked-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>