IB/mlx5: Report inner RSS capability

Add missing inner RSS support capability as part of
the RSS supported fields.

In addition change MLX5_RX_HASH_INNER to 1UL << 31 in
order to define it as unsigned.

Fixes: 309fa347 ("IB/mlx5: Add support for RSS on the inner packet")
Signed-off-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>