use descending order to remove preferred route from list

kamailio/dispatcher-role-5.2.cfg

@@ -173,12 +173,12 @@ route[DISPATCHER_PREFERRED_ROUTE]
 
     xlog("L_INFO", "$ci|log|re-ordering the dispatcher list to maintain association with $var(prefered_route)\n");    
 
-    $var(i) = 0;
-    while($var(i) < $xavp(ds_ctx=>cnt)) {
+    $var(i) = $xavp(ds_ctx=>cnt) - 1;
+    while($var(i) >= 0) {
        if($xavp(ds_dst[$var(i)]=>uri) == $var(prefered_route)) {
-          $xavp(ds_dst[$var(i)]=>*) = $null;
+          $xavp(ds_dst[$var(i)]) = $null;
        }
-       $var(i) = $var(i) + 1;
+       $var(i) = $var(i) - 1;
     }
 
     $xavp(ds_dst=>uri) = $var(prefered_route);