face: allow setting default UDP face MTU in config

refs #5138

Change-Id: Ibb3767b27aec2b046d1f41292f3d61001866f8c0
diff --git a/daemon/face/channel.cpp b/daemon/face/channel.cpp
index 8b1333e..dd3b118 100644
--- a/daemon/face/channel.cpp
+++ b/daemon/face/channel.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2019,  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,
@@ -38,6 +38,12 @@
 }
 
 void
+Channel::setDefaultMtu(size_t mtu)
+{
+  m_defaultMtu = mtu;
+}
+
+void
 connectFaceClosedSignal(Face& face, std::function<void()> f)
 {
   face.afterStateChange.connect([f = std::move(f)] (auto, FaceState newState) {