netflow: Fix memory leak in netflow_unref.

The memory leak was triggered each time on calling netflow_unref() with
containing netflow_flows. And flows need to be removed and destroyed.

Signed-off-by: Yunjian Wang <wangyunjian@huawei.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>

ofproto/netflow.c

@@ -413,6 +413,14 @@ netflow_unref(struct netflow *nf)
         atomic_count_dec(&netflow_count);
         collectors_destroy(nf->collectors);
         ofpbuf_uninit(&nf->packet);
+
+        struct netflow_flow *nf_flow, *next;
+        HMAP_FOR_EACH_SAFE (nf_flow, next, hmap_node, &nf->flows) {
+            hmap_remove(&nf->flows, &nf_flow->hmap_node);
+            free(nf_flow);
+        }
+        hmap_destroy(&nf->flows);
+
         free(nf);
     }
 }