net/mlx5: Introduce bulk reading of flow counters

This commit utilize the ability of ConnectX-4 to bulk read flow counters.
Few bulk counter queries could be done instead of issuing thousands of
firmware commands per second to get statistics of all flows set to HW,
such as those programmed when we offload tc filters.

Counters are stored sorted by hardware id, and queried in blocks (id +
number of counters).

Due to hardware requirement, start of block and number of counters in a
block must be four aligned.

Reviewed-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Amir Vadai <amir@vadai.me>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>