make sure blocklist.de-rule for Received IPs only triggers once

conf/scores.d/rbl_group.conf

@@ -168,5 +168,6 @@ symbols = {
     "RECEIVED_BLOCKLISTDE" {
         weight = 3.0;
         description = "Received address is listed in Blocklist (https://www.blocklist.de/)";
+        one_shot = true;
     }
 }