Change namespace of DummyClientFace, Signal, Segmenter

refs #3940

Change-Id: I67ca0ecb8c916aab411a2f90454e0d25925978cd
diff --git a/tests/ping/client/statistics-collector.t.cpp b/tests/ping/client/statistics-collector.t.cpp
index 9d5423a..5d3e0d3 100644
--- a/tests/ping/client/statistics-collector.t.cpp
+++ b/tests/ping/client/statistics-collector.t.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2022,  Arizona Board of Regents.
+ * Copyright (c) 2014-2023,  Arizona Board of Regents.
  *
  * This file is part of ndn-tools (Named Data Networking Essential Tools).
  * See AUTHORS.md for complete list of ndn-tools authors and contributors.
@@ -44,7 +44,7 @@
   }
 
 protected:
-  util::DummyClientFace face;
+  DummyClientFace face;
   Options pingOptions{makeOptions()};
   Ping pingProgram{face, pingOptions};
   StatisticsCollector sc{pingProgram, pingOptions};