Template proxy is not used for IPv6 subnets
When provisioning a host using the Smart Proxy template feature it's only used from the IPv4 subnet.
To reproduce, create a host with only an IPv6 subnet (that has a template proxy set) on the provisioning interface. You would expect the template proxy to be used, but instead you see the actual unattended URL.
It's because this only looks at subnet and not subnet6.