CC-5840: Add Media -> Endless retries if there is a validation error

Fixed by not adding message to retry queue if request returns a
validation specific error code (422)

airtime_mvc/application/modules/rest/controllers/MediaController.php

@@ -369,7 +369,7 @@ class Rest_MediaController extends Zend_Rest_Controller
     private function invalidDataResponse()
     {
         $resp = $this->getResponse();
-        $resp->setHttpResponseCode(400);
+        $resp->setHttpResponseCode(422);
         $resp->appendBody("ERROR: Invalid data");
     }