virtio-net: fix the memory leak in rxfilter_notify()

object_get_canonical_path() returns a gchar*, it should be freed by the
caller.
Signed-off-by: NAmos Kong <akong@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Reviewed-by: NVlad Yasevich <vyasevic@redhat.com>
Reviewed-by: NAndreas Färber <afaerber@suse.de>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

hw/net/virtio-net.c

@@ -200,16 +200,16 @@ static void rxfilter_notify(NetClientState *nc)
     VirtIONet *n = qemu_get_nic_opaque(nc);
 
     if (nc->rxfilter_notify_enabled) {
+        gchar *path = object_get_canonical_path(OBJECT(n->qdev));
         if (n->netclient_name) {
             event_data = qobject_from_jsonf("{ 'name': %s, 'path': %s }",
-                                    n->netclient_name,
-                                    object_get_canonical_path(OBJECT(n->qdev)));
+                                    n->netclient_name, path);
         } else {
-            event_data = qobject_from_jsonf("{ 'path': %s }",
-                                    object_get_canonical_path(OBJECT(n->qdev)));
+            event_data = qobject_from_jsonf("{ 'path': %s }", path);
         }
         monitor_protocol_event(QEVENT_NIC_RX_FILTER_CHANGED, event_data);
         qobject_decref(event_data);
+        g_free(path);
 
         /* disable event notification to avoid events flooding */
         nc->rxfilter_notify_enabled = 0;