app/testpmd: release flows left before port stop

app/testpmd: release flows left before port stop

According to RTE flow user guide, PMD will not keep flow rules after
port stop. Application resources that refer to flow rules become
obsolete after port stop and must not be used.
Testpmd maintains linked list of active flows for each port. Entries in
that list are allocated dynamically and must be explicitly released to
prevent memory leak.
The patch releases testpmd port flow_list that holds remaining flows
before port is stopped.

Cc: stable@dpdk.org
Signed-off-by: Gregory Etelson <getelson@nvidia.com>
Acked-by: Ori Kam <orika@nvidia.com>
Acked-by: Ajit Khaparde <ajit.khaparde@broadcom.com>