[5122] Added a comment explaining (where) client-class code was moved

src/bin/dhcp4/json_config_parser.cc

@@ -259,6 +259,8 @@ protected:
             subnet4->get4o6().setInterfaceId(opt);
             subnet4->get4o6().enabled(true);
         }
+
+        // client-class processing is now generic so in DhcpConfigParser
     }
 };