helper+model: Fix helpers to work with NFD/ndn-cxx 0.4+

Change-Id: I7ed2893acbda1458383603c0e3c154d3e841405e
Refs: #3560
diff --git a/helper/ndn-stack-helper.cpp b/helper/ndn-stack-helper.cpp
index 06dd368..4037cf8 100644
--- a/helper/ndn-stack-helper.cpp
+++ b/helper/ndn-stack-helper.cpp
@@ -330,9 +330,7 @@
 
   if (m_needSetDefaultRoutes) {
     // default route with lowest priority possible
-
-    // TODO: Restore when FibHelper is available
-    // FibHelper::AddRoute(node, "/", face, std::numeric_limits<int32_t>::max());
+    FibHelper::AddRoute(node, "/", face, std::numeric_limits<int32_t>::max());
   }
   return face;
 }