Closes #11619: Include VLANs with a null site in query during bulk interface edit for Devices > DEVICE COMPONENTS > Interfaces (#12659)

* Closes #11619: Allow VLANs without a site during multi-port edits

This commit allows users to be able to select VLANs without a site assignment
during bulk interfaces edits under Devices > DEVICE COMPONENTS > Interfaces.

Prior to this commit, only VLANs that were assigned the same site as the device
were available for selection.

* Replace 'null' with FILTERS_NULL_CHOICE_VALUE constant

---------

Co-authored-by: jeremystretch <jstretch@netboxlabs.com>

netbox/dcim/forms/bulk_edit.py

@@ -1,4 +1,5 @@
 from django import forms
+from django.conf import settings
 from django.contrib.auth.models import User
 from django.utils.translation import gettext as _
 from timezone_field import TimeZoneFormField
@@ -1292,8 +1293,13 @@ class InterfaceBulkEditForm(
                         break
 
                 if site is not None:
-                    self.fields['untagged_vlan'].widget.add_query_param('site_id', site.pk)
-                    self.fields['tagged_vlans'].widget.add_query_param('site_id', site.pk)
+                    # Query for VLANs assigned to the same site and VLANs with no site assigned (null).
+                    self.fields['untagged_vlan'].widget.add_query_param(
+                        'site_id', [site.pk, settings.FILTERS_NULL_CHOICE_VALUE]
+                    )
+                    self.fields['tagged_vlans'].widget.add_query_param(
+                        'site_id', [site.pk, settings.FILTERS_NULL_CHOICE_VALUE]
+                    )
 
             self.fields['parent'].choices = ()
             self.fields['parent'].widget.attrs['disabled'] = True