title: django: filter queryset when 2 fields have same value
body: <p>I have a model which has 2 fields like,</p>
  
  <pre><code>pickup_station_id = models.IntegerField(null=True)
  drop_station_id = models.IntegerField(null=True)
  </code></pre>
  
  <p>I want a filter in admin which can filter the queryset based on,</p>
  
  <ul>
  <li>pickup and drop ids are different</li>
  <li>pickup and drop ids are same</li>
  </ul>
  
  <p>How can I get a queryset based on these conditions?</p>
  
  <p>I mean, something like this,</p>
  
  <pre><code>Mymodel.objects.filter(pickup_station_id==drop_station_id)
  
  Mymodel.objects.filter(pickup_station_id!=drop_station_id)
  </code></pre>