fw+table: workaround bogus doxygen warnings

Change-Id: I0a093658f4b27620ba9731a0640ca71c3d03360a
diff --git a/daemon/table/pit-entry.hpp b/daemon/table/pit-entry.hpp
index 6287e44..bc4f1d3 100644
--- a/daemon/table/pit-entry.hpp
+++ b/daemon/table/pit-entry.hpp
@@ -241,7 +241,7 @@
 
   name_tree::Entry* m_nameTreeEntry = nullptr;
 
-  friend name_tree::Entry;
+  friend ::nfd::name_tree::Entry;
 };
 
 } // namespace nfd::pit