fw+table: workaround bogus doxygen warnings

Change-Id: I0a093658f4b27620ba9731a0640ca71c3d03360a
diff --git a/daemon/table/measurements-entry.hpp b/daemon/table/measurements-entry.hpp
index 56825b6..a3983ae 100644
--- a/daemon/table/measurements-entry.hpp
+++ b/daemon/table/measurements-entry.hpp
@@ -62,8 +62,8 @@
 
   name_tree::Entry* m_nameTreeEntry = nullptr;
 
+  friend ::nfd::name_tree::Entry;
   friend Measurements;
-  friend name_tree::Entry;
 };
 
 } // namespace nfd::measurements