face: allow setting default UDP face MTU in config

refs #5138

Change-Id: Ibb3767b27aec2b046d1f41292f3d61001866f8c0
diff --git a/daemon/face/udp-channel.hpp b/daemon/face/udp-channel.hpp
index 89540de..c3f696d 100644
--- a/daemon/face/udp-channel.hpp
+++ b/daemon/face/udp-channel.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2018,  Regents of the University of California,
+ * Copyright (c) 2014-2021,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -49,7 +49,8 @@
    */
   UdpChannel(const udp::Endpoint& localEndpoint,
              time::nanoseconds idleTimeout,
-             bool wantCongestionMarking);
+             bool wantCongestionMarking,
+             size_t defaultMtu);
 
   bool
   isListening() const override