model+helper+examples: Enable configurability of NFD parameters using StackHelper

Refs: #2353, #2220
diff --git a/examples/ndn-congestion-topo-plugin.cpp b/examples/ndn-congestion-topo-plugin.cpp
index 11fed0e..ba40c7a 100644
--- a/examples/ndn-congestion-topo-plugin.cpp
+++ b/examples/ndn-congestion-topo-plugin.cpp
@@ -57,8 +57,7 @@
 
   // Install NDN stack on all nodes
   ndn::StackHelper ndnHelper;
-  ndnHelper.SetContentStoreChoice(false);
-  ndnHelper.SetContentStore("ns3::ndn::cs::Lru", "MaxSize", "10000");
+  ndnHelper.SetOldContentStore("ns3::ndn::cs::Lru", "MaxSize", "10000");
   ndnHelper.InstallAll();
 
   // Choosing forwarding strategy