Compilation fixes after upgrade to NFD 0.6.6 and removal of old-style CS

Change-Id: I5472ae71675d8419d8d6c70990182ef028803087
diff --git a/examples/ndn-tree-with-l2tracer.cpp b/examples/ndn-tree-with-l2tracer.cpp
index ab80675..200ae1a 100644
--- a/examples/ndn-tree-with-l2tracer.cpp
+++ b/examples/ndn-tree-with-l2tracer.cpp
@@ -38,7 +38,8 @@
   /****************************************************************************/
   // Install NDN stack on all nodes
   ndn::StackHelper ndnHelper;
-  ndnHelper.SetOldContentStore("ns3::ndn::cs::Lru", "MaxSize", "1000");
+  ndnHelper.setPolicy("nfd::cs::lru");
+  ndnHelper.setCsSize(1000);
   ndnHelper.InstallAll();
   /****************************************************************************/
   // Installing global routing interface on all nodes