net/mlx5: optimize flow counter handle type

net/mlx5: optimize flow counter handle type

Currently, DV and verbs counters are both changed to indexed. It means
while creating the flow with counter, flow can save the indexed value to
address the counter.

Save the 4 bytes indexed value in the rte_flow instead of 8 bytes
pointer helps to save memory with millions of flows.

Signed-off-by: Suanming Mou <suanmingm@mellanox.com>
Acked-by: Matan Azrad <matan@mellanox.com>