net/mlx5: fix RSS hash update

net/mlx5: fix RSS hash update

Few bugs fixes in both configuration get and hash update where inputs
are not handled as expected by the ethdev layer.

RSS structure may not be totally usable, the PMD should try to take as
most information from it has it can when it is an hash update or it
should try to fill as most as possible in the configuration get.
This means that in the RSS configuration structure, the memory space for
the RSS hash key may not be present, but the PMD should consider the
hash field valid and process/set it.

Fixes: 29c1d8bb3e79 ("net/mlx5: handle a single RSS hash key for all protocols")

Signed-off-by: Nelio Laranjeiro <nelio.laranjeiro@6wind.com>
Acked-by: Yongseok Koh <yskoh@mellanox.com>