net/mlx4: drop RSS support

net/mlx4: drop RSS support

The Verbs RSS API used in this PMD is now obsolete. It is superseded by an
enhanced API with fewer constraints already used in the mlx5 PMD.

Drop RSS support in preparation for a major refactoring. The ability to
configure several Rx queues is retained, these can be targeted directly by
creating specific flow rules.

There is no need for "ignored" Rx queues anymore since their number is no
longer limited to powers of two.

Signed-off-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>