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/tests/daemon/face/dummy-transport.hpp b/tests/daemon/face/dummy-transport.hpp
index c5c5268..0e76d47 100644
--- a/tests/daemon/face/dummy-transport.hpp
+++ b/tests/daemon/face/dummy-transport.hpp
@@ -72,6 +72,13 @@
     this->receive(Packet(std::move(block)));
   }
 
+protected:
+  virtual void
+  beforeChangePersistency(ndn::nfd::FacePersistency newPersistency) DECL_OVERRIDE
+  {
+    // accept everything
+  }
+
 private:
   virtual void
   doClose() DECL_OVERRIDE