net/mlx4: add RSS support outside flow API

net/mlx4: add RSS support outside flow API

Bring back support for automatic RSS with the default flow rules when not
in isolated mode. Balancing is done according to unspecified default
settings, as was the case before this entire rework.

Since the number of queues part of RSS contexts is limited to power of two
values, the number of configured queues is rounded down to its previous
power of two; extra queues are silently discarded. This does not prevent
dedicated flow rules from targeting them.

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