Add symbol for DNSWL

conf/modules.conf

@@ -184,6 +184,7 @@ rbl {
         rbl = "list.dnswl.org";
         unknown = true;
         returncodes {
+            RCVD_IN_DNSWL_NONE = "127.0.%d+.0";
             RCVD_IN_DNSWL_LOW = "127.0.%d+.1";
             RCVD_IN_DNSWL_MED = "127.0.%d+.2";
             RCVD_IN_DNSWL_HI  = "127.0.%d+.3";