Behavior for getting available ips in v6 prefixes differ between api and frontend

[jweiher]

NetBox version

v.2.11.1

Python version

3.9

Steps to Reproduce

1. Create a v6 prefix
2. Open ip addresses tab
3. See that the frontend suggests (correctly) that :: (e.g. the 0-th ip in the net) is available, which is correct for v6
4. Use /ipam/prefixes/{id}/available-ips/ via API for the same prefix - the first ip shown is ::1

Expected Behavior

The expected behavior would be that at least the api and the frontend behave the same.

Observed Behavior

API and Frontend behave different. The problem is probably due to different "get available ip" algorithms being implemented. The frontend view uses code from ipam/utils.py and the api uses the code from the prefix model. In my opinion there should only be one place in the codebase where this is implemented.