face: override Transport::beforeChangePersistency in all subclasses

This commit also adds the final specifier to some Transport
subclasses in order to improve code generation.

Change-Id: If2979fa1614476a98019ba79cee3961663fc447b
Refs: #3318
diff --git a/daemon/face/websocket-transport.cpp b/daemon/face/websocket-transport.cpp
index 4fbed81..cf3da37 100644
--- a/daemon/face/websocket-transport.cpp
+++ b/daemon/face/websocket-transport.cpp
@@ -56,7 +56,8 @@
   NFD_LOG_FACE_INFO("Creating transport");
 }
 
-void WebSocketTransport::beforeChangePersistency(ndn::nfd::FacePersistency newPersistency)
+void
+WebSocketTransport::beforeChangePersistency(ndn::nfd::FacePersistency newPersistency)
 {
   if (newPersistency != ndn::nfd::FACE_PERSISTENCY_ON_DEMAND) {
     BOOST_THROW_EXCEPTION(