Enabling app-layer tracing

Network-layer tracing is not working yet (needs a couple of attributes
to be implemented)
diff --git a/model/annotated-topology-reader.cc b/model/annotated-topology-reader.cc
index 6553f86..15c0d6b 100644
--- a/model/annotated-topology-reader.cc
+++ b/model/annotated-topology-reader.cc
@@ -59,7 +59,7 @@
 {
   NS_LOG_FUNCTION (this);
 
-  // SetMobilityModel ("ns3::ConstantPositionMobilityModel");
+  SetMobilityModel ("ns3::ConstantPositionMobilityModel");
 }
     
 void