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/table/fib-nexthop.cpp b/daemon/table/fib-nexthop.cpp
index 06bbdcb..178d853 100644
--- a/daemon/table/fib-nexthop.cpp
+++ b/daemon/table/fib-nexthop.cpp
@@ -6,7 +6,7 @@
 
 #include "fib-nexthop.hpp"
 
-namespace ndn {
+namespace nfd {
 namespace fib {
 
 NextHop::NextHop(shared_ptr<Face> face)
@@ -38,4 +38,4 @@
 }
 
 } // namespace fib
-} // namespace ndn
+} // namespace nfd