net/mlx4: add RSS flow rule action support

net/mlx4: add RSS flow rule action support

This patch dissociates single-queue indirection tables and hash QP objects
from Rx queue structures to relinquish their control to users through the
RSS flow rule action, while simultaneously allowing multiple queues to be
associated with RSS contexts.

Flow rules share identical RSS contexts (hashed fields, hash key, target
queues) to save on memory and other resources. The trade-off is some added
complexity due to reference counters management on RSS contexts.

The QUEUE action is re-implemented on top of an automatically-generated
single-queue RSS context.

The following hardware limitations apply to RSS contexts:

- The number of queues in a group must be a power of two.
- Queue indices must be consecutive, for instance the [0 1 2 3] set is
  allowed, however [3 2 1 0], [0 2 1 3] and [0 0 1 1 2 3 3 3] are not.
- The first queue of a group must be aligned to a multiple of the context
  size, e.g. if queues [0 1 2 3 4] are defined globally, allowed group
  combinations are [0 1] and [2 3]; groups [1 2] and [3 4] are not
  supported.
- RSS hash key, while configurable per context, must be exactly 40 bytes
  long.
- The only supported hash algorithm is Toeplitz.

Signed-off-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>
Acked-by: Nelio Laranjeiro <nelio.laranjeiro@6wind.com>