RDMA/mlx5: Add steering support in optional flow counters

RDMA/mlx5: Add steering support in optional flow counters

Adding steering infrastructure for adding and removing optional counter.
This allows to add and remove the counters dynamically in order not to
hurt performance.

Link: https://lore.kernel.org/r/20211008122439.166063-12-markzhang@nvidia.com
Signed-off-by: Aharon Landau <aharonl@nvidia.com>
Reviewed-by: Maor Gottlieb <maorg@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Mark Zhang <markzhang@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>