fix the stats a little for not accepting udp scrapes

opentracker.c

@@ -654,6 +654,10 @@ static void handle_udp4( int64 serversocket ) {
         ot_overall_udp_successfulannounces++;
       }
       break;
+
+    case 2: /* This is a scrape action */
+      ot_overall_udp_connections--; // subtract again because we don't answer scrapes but it is also not an error
+      break;
   }
 }