network-ip-availabilities api return data is incorrect

[ZhouHeng]

This bug tracker is for errors with the documentation, use the following as a template and remove or add fields as you see fit. Convert [ ] into [x] to check boxes:

- [ ] This doc is inaccurate in this way: ______
- [ ] This is a doc addition request.
- [ ] I have a fix to the document that I can paste below including example: input and output.

If you have a troubleshooting or support issue, use the following resources:

 - Ask OpenStack: http://ask.openstack.org
 - The mailing list: http://lists.openstack.org
 - IRC: 'openstack' channel on Freenode

-----------------------------------
Release: on 2019-07-29 13:09:43
SHA: aaae83acaac5f58918ff53613b4de20bbfe30d81
Source: https://opendev.org/openstack/neutron-lib/src/api-ref/source/v2/index.rst
URL: https://docs.openstack.org/api-ref/network/v2/index.html

[ZhouHeng (zhouhenglc)]

First I create a network and a subnet. network_id=0c557c5f-acf6-44c4-8c1c-cc12672d4d4f
second I update subnet with allocation_pools=[]

then I call api /v2.0/network-ip-availabilities/0c557c5f-acf6-44c4-8c1c-cc12672d4d4f
api return:
{"network_ip_availability": {"used_ips": 1, "subnet_ip_availability": [{"used_ips": 1, "subnet_id": "a5b694f7-7054-4ecc-8447-8e9a7a15c5f0", "subnet_name": "ZhNet-Subnet", "ip_version": 4, "cidr": "192.168.120.0/24", "total_ips": 256}], "network_id": "0c557c5f-acf6-44c4-8c1c-cc12672d4d4f", "tenant_id": "2fb75a1bedac449d904f71fbea5cd1d2", "total_ips": 256, "project_id": "2fb75a1bedac449d904f71fbea5cd1d2", "network_name": "ZhNet"}}
this result tell me: I have 256 available IPs in subnet. but I couldn't create a port successfully in this network.

[ZhouHeng (zhouhenglc)]

The total number of IPs should be = the number of unions of address pool IP and used IP.
Because address pools are allowed to be deleted. There are also addresses outside the address pool, such as router addresses.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/674723

[OpenStack Infra (hudson-openstack)]

Change abandoned by Slawek Kaplonski (<email address hidden>) on branch: master
Review: https://review.opendev.org/674723
Reason: This review is > 4 weeks without comment, and failed Jenkins the last time it was checked. We are abandoning this for now. Feel free to reactivate the review by pressing the restore button and leaving a 'recheck' comment to get fresh test results.