net/mlx5: flow counter support

net/mlx5: flow counter support

Example for setting rule for counting packets with dest
ip = 192.168.3.1 in testpmd:

testpmd: flow create 0 ingress pattern eth / ipv4 dst is 192.168.3.1
/ end actions queue index 0 / count / end

Reading the number of packets and bytes for the rule:

testpmd: flow query 0 0 count

Note: This feature is only supported starting Mellanox OFED 4.2

Signed-off-by: Ori Kam <orika@mellanox.com>
Signed-off-by: Nelio Laranjeiro <nelio.laranjeiro@6wind.com>
Acked-by: Yongseok Koh <yskoh@mellanox.com>