net/filter: fix nf->netdev_id leak

Cc: Jason Wang <jasowang@redhat.com>
Cc: qemu-stable@nongnu.org
Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

net/filter.c

@@ -204,6 +204,7 @@ static void netfilter_finalize(Object *obj)
     if (nf->netdev && !QTAILQ_EMPTY(&nf->netdev->filters)) {
         QTAILQ_REMOVE(&nf->netdev->filters, nf, next);
     }
+    g_free(nf->netdev_id);
 }
 
 static void netfilter_class_init(ObjectClass *oc, void *data)