net/mlx5: Introduce port selection namespace

Add new port selection flow steering namespace. Flow steering rules in
this namespaceare are used to determine the physical port for egress
packets.

Signed-off-by: Maor Gottlieb <maorg@nvidia.com>
Reviewed-by: Mark Bloch <mbloch@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>