model: add queue length congestion detection and signaling

add PCON consumer app

refs #4578

Change-Id: I1b04e3d123510b1ed6134a708c2710ebbb217167
diff --git a/model/ndn-net-device-transport.hpp b/model/ndn-net-device-transport.hpp
index 09a08ed..e68382d 100644
--- a/model/ndn-net-device-transport.hpp
+++ b/model/ndn-net-device-transport.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
-/**
- * Copyright (c) 2011-2016  Regents of the University of California.
+/*
+ * Copyright (c) 2011-2018  Regents of the University of California.
  *
  * This file is part of ndnSIM. See AUTHORS for complete list of ndnSIM authors and
  * contributors.
@@ -54,6 +54,9 @@
   Ptr<NetDevice>
   GetNetDevice() const;
 
+  virtual ssize_t
+  getSendQueueLength() final;
+
 private:
   virtual void
   doClose() override;