net/mlx5: add meter statistics read and update
net/mlx5: add meter statistics read and update

This commit add the meter statistics read and update to check the meter
statistics.

New internal functions in rte_mtr_ops callback:
1. stats_update()
2. stats_read()

Signed-off-by: Suanming Mou <ffae22abfb44f67da81795938a64e892585787cc@mellanox.com>
Acked-by: Matan Azrad <6969f5f553ad7652679a585a85d7321babc90464@mellanox.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk