face: refactor handling of LinkType face trait

This commit also includes some cleanups, fixes EthernetFace to report
the correct LinkType, and makes (get|set)Description non-virtual.

Change-Id: I53909d7bfa02a92641b523a766359413c966aae6
Refs: #2563
diff --git a/daemon/face/multicast-udp-face.cpp b/daemon/face/multicast-udp-face.cpp
index 9eb38c3..910f1cb 100644
--- a/daemon/face/multicast-udp-face.cpp
+++ b/daemon/face/multicast-udp-face.cpp
@@ -35,13 +35,10 @@
                                    const shared_ptr<MulticastUdpFace::protocol::socket>& sendSocket,
                                    const MulticastUdpFace::protocol::endpoint& localEndpoint,
                                    const MulticastUdpFace::protocol::endpoint& multicastEndpoint)
-  : DatagramFace<protocol, Multicast>(FaceUri(multicastEndpoint),
-                                      FaceUri(localEndpoint),
-                                      recvSocket, false)
+  : DatagramFace(FaceUri(multicastEndpoint), FaceUri(localEndpoint), recvSocket)
   , m_multicastGroup(multicastEndpoint)
   , m_sendSocket(sendSocket)
 {
-  NFD_LOG_FACE_INFO("Creating face");
 }
 
 const MulticastUdpFace::protocol::endpoint&
@@ -80,10 +77,4 @@
   sendBlock(data.wireEncode());
 }
 
-bool
-MulticastUdpFace::isMultiAccess() const
-{
-  return true;
-}
-
 } // namespace nfd