Restore filterset_form on DeviceInterfacesView

Removing it dropped the Saved Filters dropdown from the Interfaces tab
(table_controls_htmx.html gates the dropdown on filter_form). Now that
the full filter panel is no longer rendered in object_children.html,
restoring filterset_form only populates filter_form.filter_id for the
saved-filter select — none of the heavy form fields are rendered.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

netbox/dcim/views.py

@@ -2742,6 +2742,7 @@ class DeviceInterfacesView(DeviceComponentsView):
     child_model = Interface
     table = tables.DeviceInterfaceTable
     filterset = filtersets.InterfaceFilterSet
+    filterset_form = forms.InterfaceFilterForm
     actions = (EditObject, DeleteObject, BulkEdit, BulkRename, BulkDisconnect, BulkDelete)
     template_name = 'dcim/device/interfaces.html'
     tab = ViewTab(