Multiple IPs from ipv6 subnets on the associated network are allocated for port creation

[sunzuohua]

From the spec[1], we will get one IP address from one of the v6 subnets.

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Port-create operations without an explicit list of fixed IPs: There will be no change from the current design. When a port-create operation does not include an explicit list of fixed IPs, the following subnets on the associated network will be associated with the port:

One subnet from all IPv4 subnets
One subnet from all IPv6 DHCPv6-stateful subnets
All SLAAC-enabled subnets
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But actually we get multiple IPs from all of the v6 subnets.
[1]https://specs.openstack.org/openstack/neutron-specs/specs/kilo/multiple-ipv6-prefixes.html