face: allow GenericLinkService to override MTU

refs #5056

Change-Id: I8eb2dd732b1431e0e809deb53792a14be1698ff1
diff --git a/daemon/face/unicast-ethernet-transport.hpp b/daemon/face/unicast-ethernet-transport.hpp
index 63d74e9..49c9d48 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) 2014-2019,  Regents of the University of California,
+ * Copyright (c) 2014-2020,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -43,8 +43,7 @@
   UnicastEthernetTransport(const ndn::net::NetworkInterface& localEndpoint,
                            const ethernet::Address& remoteEndpoint,
                            ndn::nfd::FacePersistency persistency,
-                           time::nanoseconds idleTimeout,
-                           optional<ssize_t> overrideMtu = {});
+                           time::nanoseconds idleTimeout);
 
 protected:
   bool