fix(controller): guard missing skip_push_update_on_save in register

DeviceRegisterView._update_device_name calls
``device.skip_push_update_on_save()`` when an agent re-registers with a
hostname different from the MAC address. That method is referenced in
the view but is not implemented on the Device model, so every such
re-registration crashes with an HTTP 500:

    AttributeError: 'Device' object has no attribute 'skip_push_update_on_save'

This breaks the consistent_registration / factory-reset workflow: a
router that loses its local UUID/key after a firstboot tries to
re-register and gets a 500 error instead of finding its existing record
by consistent_key.

Wrap the call in ``getattr`` so the registration succeeds whether the
helper method exists or not. The actual method can be re-introduced
separately without changing this site.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Codex

openwisp_controller/config/controller/views.py

@@ -538,7 +538,15 @@ def _update_device_name(self, request, device):
         normalized_name = name.replace(":", "").replace("-", "").lower()
         if normalized_name != normalized_mac:
             device.name = name
-            device.skip_push_update_on_save()
+            # NOTE: upstream openwisp-controller 1.2 calls
+            # ``device.skip_push_update_on_save()`` here, but that method
+            # was never implemented on the Device model, causing every
+            # re-registration with a non-MAC hostname to crash with
+            # AttributeError. We guard the call so missing methods don't
+            # break factory-reset re-registration.
+            skip = getattr(device, "skip_push_update_on_save", None)
+            if callable(skip):
+                skip()
 
 
 class GetVpnView(SingleObjectMixin, View):