apps + examples: Enabling NACK support

Change-Id: I3d16bcf29f4858049d1040a3e421e1c7151b2bb2
Refs: #3871
diff --git a/apps/ndn-consumer-zipf-mandelbrot.hpp b/apps/ndn-consumer-zipf-mandelbrot.hpp
index f973240..cdf58a2 100644
--- a/apps/ndn-consumer-zipf-mandelbrot.hpp
+++ b/apps/ndn-consumer-zipf-mandelbrot.hpp
@@ -63,6 +63,7 @@
 
   virtual void
   SendPacket();
+
   uint32_t
   GetNextSeq();