Comment 2 for bug 1710833

The current behaviour is to keep the already assigned fixed_ips during update[1]. As that is the only thing that's changed in the template above, we're sending an empty dict '{}' and neutron throws an error in that case.

[1] https://github.com/openstack/heat/blob/master/heat/engine/resources/openstack/neutron/port.py#L462