net/mlx5: Add priorities for counters in RDMA namespaces

Add additional flow steering priorities in the RDMA namespace.
This allows adding flow counters to count filtered RDMA traffic and then
continue processing in the regular RDMA steering flow.

Signed-off-by: Aharon Landau <aharonl@nvidia.com>
Reviewed-by: Maor Gottlieb <maorg@nvidia.com>
Signed-off-by: Mark Zhang <markzhang@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>