mgmt+face: allow MTU of datagram faces to be overridden

refs #4005

Change-Id: I01d98b88cdee41b633f6fb9a5600088efe8de749
diff --git a/daemon/face/unicast-ethernet-transport.hpp b/daemon/face/unicast-ethernet-transport.hpp
index 19617e3..5a148c9 100644
--- a/daemon/face/unicast-ethernet-transport.hpp
+++ b/daemon/face/unicast-ethernet-transport.hpp
@@ -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,
@@ -44,7 +44,8 @@
   UnicastEthernetTransport(const ndn::net::NetworkInterface& localEndpoint,
                            const ethernet::Address& remoteEndpoint,
                            ndn::nfd::FacePersistency persistency,
-                           time::nanoseconds idleTimeout);
+                           time::nanoseconds idleTimeout,
+                           optional<ssize_t> overrideMtu = {});
 
 protected:
   bool