iptrunk_checks - optical diff

only produce diff when called from `iptrun_migration`, and `new_node` is
therefore defined.
the diff will be skipped if the role called from elsewhere.

geant/gap_ansible/roles/iptrunk_checks/tasks/main.yml

@@ -152,5 +152,7 @@
   when: >-
     check == "optical_post"
     and
+    new_node is defined
+    and
     inventory_hostname != new_node.router.router_fqdn
   ansible.builtin.include_tasks: diff_optical_results.yaml