net/mlx5: replace flow list with indexed pool

net/mlx5: replace flow list with indexed pool

The flow list is used to save the create flows and to be used only
when port closes all the flows need to be flushed.

This commit takes advantage of the index pool foreach operation to
flush all the allocated flows.

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