Network hangs during MQTT test

Kernel
7

mqtt_delete_request() method has no protection against queue loops. I didn’t figure out how loops are created during putting requests into the queue, but breaking such loops fix was trivial and eliminated the problem

/**
 * Delete request item
 * @param r Request item to delete
 */
static void
mqtt_delete_request(struct mqtt_request_t *r)
{
  if (r != NULL) {
      // Break potential loops
      if (r->next != r) {
          r->next = r;
      }
      else {
          r->next = NULL;
      }
  }
}