doc: add flow dump to mlx5 guide
doc: add flow dump to mlx5 guide

Guide of mlx5 is updated on how to dump HW flows.

Signed-off-by: Xueming Li <a578f76ca98b1dec92e0d1baef814b93f3f2f3b4@mellanox.com>
Signed-off-by: Xiaoyu Min <03352a7947822e04037757091119acfbe3910106@mellanox.com>

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