Issue #25   Replacing usage of TCP RTT estimator with a customized version

In the current commit, RTT estimator does not implement Karn's algorithm
and takes into account all RTT samples, including ambiguous samples from
retransmitted Interests.
diff --git a/apps/ndn-consumer.h b/apps/ndn-consumer.h
index 970da4c..75705cd 100644
--- a/apps/ndn-consumer.h
+++ b/apps/ndn-consumer.h
@@ -27,8 +27,7 @@
 #include "ns3/ndn-name-components.h"
 #include "ns3/nstime.h"
 #include "ns3/data-rate.h"
-//#include "ns3/internet-module.h"
-#include "ns3/rtt-estimator.h"
+#include "ns3/ndn-rtt-estimator.h"
 
 #include <set>
 #include <map>