testutils: use group_mod subclasses
diff --git a/src/python/oftest/testutils.py b/src/python/oftest/testutils.py
index 743e4e7..e8498d5 100644
--- a/src/python/oftest/testutils.py
+++ b/src/python/oftest/testutils.py
@@ -55,8 +55,7 @@
     """
 
     logging.info("Deleting all groups")
-    msg = ofp.message.group_mod(
-        command=ofp.OFPGC_DELETE, group_id=ofp.OFPG_ALL)
+    msg = ofp.message.group_delete(group_id=ofp.OFPG_ALL)
     ctrl.message_send(msg)
     do_barrier(ctrl)