src: Changing namespace ndn to namespace nfd

Also, this commit imports used classes from ::ndn namespace (from
NDN-CPP library) directly to ::nfd namespace.

refs: #1163

Change-Id: I9cc9d72e00af495b4ed0c84e6d418a7c9ba986cb
diff --git a/daemon/face/tcp-face.cpp b/daemon/face/tcp-face.cpp
index eb3ac94..79f9b8c 100644
--- a/daemon/face/tcp-face.cpp
+++ b/daemon/face/tcp-face.cpp
@@ -6,7 +6,7 @@
 
 #include "tcp-face.hpp"
 
-namespace ndn {
+namespace nfd {
 
 TcpFace::TcpFace(FaceId id,
                  const shared_ptr<TcpFace::protocol::socket>& socket)
@@ -34,4 +34,4 @@
   // anything else should be done here?
 }
 
-} // namespace ndn
+} // namespace nfd