also clear the prefer setting when filter is binned

Netdisco/share/views/js/device.js

@@ -54,6 +54,7 @@
     // handler for trashcan icon in port filter box
     $('.nd_field-clear-icon').click(function() {
       portfilter.val('');
+      $('#nd_ports-form-prefer-field').attr('value', '');
       $('#ports_form').trigger('submit');
       device_form_state(portfilter); // will hide copy icons
     });