vlans: enslave L2 interfaces to device bridge if it exists

Only used on Cumulus switches.

vlans.py

@@ -139,6 +139,9 @@ class SetVLANScript(Script):
 
         for port in all_ports:
             port.enabled = data['enable']
+            # ensure interface is enslaved to the bridge if it exists
+            if bridge := port.device.interfaces.filter(name='bridge'):
+                port.bridge = bridge[0]
             if tagged_vlans:
                 port.mode = 'tagged'
                 port.save()