face: EthernetTransport: use MTU provided by ndn::net::NetworkInterface

Change-Id: I949f054625ae6584d99505ea3fea2c4ab65b9cfb
Refs: #4021
diff --git a/daemon/face/multicast-ethernet-transport.cpp b/daemon/face/multicast-ethernet-transport.cpp
index b4adea0..b7bbdc2 100644
--- a/daemon/face/multicast-ethernet-transport.cpp
+++ b/daemon/face/multicast-ethernet-transport.cpp
@@ -61,6 +61,7 @@
   this->setScope(ndn::nfd::FACE_SCOPE_NON_LOCAL);
   this->setPersistency(ndn::nfd::FACE_PERSISTENCY_PERMANENT);
   this->setLinkType(linkType);
+  this->setMtu(localEndpoint.getMtu());
 
   NFD_LOG_FACE_INFO("Creating transport");