net/mlx5: SD, Introduce SD lib

Add Socket-Direct API with empty/minimal implementation.
We fill-in the implementation gradually in downstream patches.

Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Gal Pressman <gal@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>