face: congestion detection in TCP, UDP, and Unix socket transports

refs #4362

Change-Id: Idaa5d65e1f33663d95bad56de42640183b2cda6d
diff --git a/daemon/face/transport.cpp b/daemon/face/transport.cpp
index 9c054fa..863b2b3 100644
--- a/daemon/face/transport.cpp
+++ b/daemon/face/transport.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
-/**
- * Copyright (c) 2014-2017,  Regents of the University of California,
+/*
+ * Copyright (c) 2014-2018,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -63,6 +63,7 @@
   , m_persistency(ndn::nfd::FACE_PERSISTENCY_NONE)
   , m_linkType(ndn::nfd::LINK_TYPE_NONE)
   , m_mtu(MTU_INVALID)
+  , m_sendQueueCapacity(QUEUE_UNSUPPORTED)
   , m_state(TransportState::UP)
   , m_expirationTime(time::steady_clock::TimePoint::max())
 {
@@ -125,6 +126,12 @@
   m_service->receivePacket(std::move(packet));
 }
 
+ssize_t
+Transport::getSendQueueLength()
+{
+  return QUEUE_UNSUPPORTED;
+}
+
 bool
 Transport::canChangePersistencyTo(ndn::nfd::FacePersistency newPersistency) const
 {