face: process face_system.udp config section in UdpFactory

refs #3904

Change-Id: I8edf69c152f7c164cbab2b482d6b138cbf89d3e2
diff --git a/daemon/face/udp-protocol.hpp b/daemon/face/udp-protocol.hpp
index 5f7c25a..f716658 100644
--- a/daemon/face/udp-protocol.hpp
+++ b/daemon/face/udp-protocol.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /**
- * Copyright (c) 2014-2016,  Regents of the University of California,
+ * Copyright (c) 2014-2017,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -31,10 +31,21 @@
 namespace nfd {
 namespace udp {
 
+typedef boost::asio::ip::udp::endpoint Endpoint;
+
 /** \brief computes maximum payload size in a UDP packet
  */
 ssize_t
-computeMtu(const boost::asio::ip::udp::endpoint& localEndpoint);
+computeMtu(const Endpoint& localEndpoint);
+
+/** \return default multicast group: 224.0.23.170:56363
+ */
+inline Endpoint
+getDefaultMulticastGroup()
+{
+  // 224.0.23.170:56363
+  return {boost::asio::ip::address_v4(0xE00017AA), 56363};
+}
 
 } // namespace udp
 } // namespace nfd