mlx5ib: Fix RSS Toeplitz setup to be aligned with the HW specification

The specification for the Toeplitz function doesn't require to set the key
explicitly to be symmetric. In case a symmetric functionality is required
a symmetric key can be simply used.

Wrongly forcing the algorithm to symmetric causes the wrong packet
distribution and a performance degradation.

Link: https://lore.kernel.org/r/20190723065733.4899-7-leon@kernel.org
Fixes: 28d6137008b2 ("IB/mlx5: Add RSS QP support")
Signed-off-by: Yishai Hadas <yishaih@mellanox.com>
Reviewed-by: Alex Vainman <alexv@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

[khng: cherry-picked from Linux
b7165bd0d6cbb93732559be6ea8774653b204480]

Sponsored by: Juniper Networks, Inc.
MFC after: 7 days
Reviewed by: kib, zlei
Differential Revision: https://reviews.freebsd.org/D42178

(cherry picked from commit 813d981e1e78daffde4b2a05df35d054fcb4343f)