Comment 7 for bug 1796074

Relaying what I said in the nova change review, nova could chunk the requests to neutron if there are more than some limit of subnet IDs, we do that elsewhere:

https://github.com/openstack/nova/blob/e37de17701168054484218e9618ed1cd21784047/nova/network/security_group/neutron_driver.py#L317

But the patch from melwitt does help with the immediate issue.