net/mlx5e: Create struct mlx5e_rss_params_hash

This commit introduces a new struct to store RSS hash parameters: hash
function and hash key. The existing usages are changed to use the new
struct.

Signed-off-by: Maxim Mikityanskiy <maximmi@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>