mlx5: fix hash Rx queue type in RSS mode

mlx5: fix hash Rx queue type in RSS mode

Only seen since IPv6 RSS support was added, confusion about the purpose of
the hash_rxq_type_from_n() function has caused it to return invalid hash RX
queue types.

Refactor function for its intended purpose, rename it
hash_rxq_type_from_pos() and update comment with a better description.

Fixes: a76133214d88 ("mlx5: use separate indirection table for default hash Rx queue")

Reported-by: Olga Shern <olgas@mellanox.com>
Signed-off-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>
Signed-off-by: Nelio Laranjeiro <nelio.laranjeiro@6wind.com>