net/mlx5: support basic meter operations

This commit add the basic meter operations for meter create and destroy.

New internal functions in rte_mtr_ops callback:
1. create()
2. destroy()

The create() callback will create the corresponding flow rules on the
meter table.
The destroy() callback destroys the flow rules on the meter table.

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