tests+ci: Add and enable a partial unit test coverage

Change-Id: I6dbc5cf4d68679bd6f943322f572313884c8aef7
Refs: #2369
diff --git a/model/ndn-global-router.cpp b/model/ndn-global-router.cpp
index 136c388..de853b7 100644
--- a/model/ndn-global-router.cpp
+++ b/model/ndn-global-router.cpp
@@ -89,11 +89,11 @@
   return m_localPrefixes;
 }
 
-// void
-// GlobalRouter::AddIncidencyChannel (Ptr< NdnFace > face, Ptr< Channel > channel)
-// {
-//   m_incidenciesChannel.push_back (make_tuple (face, channel));
-// }
+void
+GlobalRouter::clear()
+{
+  m_idCounter = 0;
+}
 
 } // namespace ndn
 } // namespace ns3