face: Fixing bug with InternalFace considered not local and changing "isLocal" method to be pure virtual

This way the decision about the face locality has to be done explicitly
inside specific face implementation and potentially avoids problems.

Change-Id: I5219cce87385313546453d14a5a7ca4542893911
diff --git a/daemon/face/tcp-face.hpp b/daemon/face/tcp-face.hpp
index 98593a0..c41f601 100644
--- a/daemon/face/tcp-face.hpp
+++ b/daemon/face/tcp-face.hpp
@@ -23,6 +23,9 @@
 
   explicit
   TcpFace(const shared_ptr<protocol::socket>& socket);
+
+  virtual bool
+  isLocal() const;
 };
 
 } // namespace nfd