apps + examples: Enabling NACK support

Change-Id: I3d16bcf29f4858049d1040a3e421e1c7151b2bb2
Refs: #3871
diff --git a/apps/ndn-consumer.cpp b/apps/ndn-consumer.cpp
index 3a1ec45..3ed9355 100644
--- a/apps/ndn-consumer.cpp
+++ b/apps/ndn-consumer.cpp
@@ -253,6 +253,16 @@
 }
 
 void
+Consumer::OnNack(shared_ptr<const lp::Nack> nack)
+{
+  /// tracing inside
+  App::OnNack(nack);
+
+  NS_LOG_INFO("NACK received for: " << nack->getInterest().getName()
+              << ", reason: " << nack->getReason());
+}
+
+void
 Consumer::OnTimeout(uint32_t sequenceNumber)
 {
   NS_LOG_FUNCTION(sequenceNumber);