device: use a separate conflict array for each address family when checking manual IP config

Summary

This commit moves the conflicts variable into the for loop, so that a new array is used for each address family.

Purpose

Fixes RHEL-11598, RHEL-1411. I suspect these tests are failing due to the conflicts array being used for IPv4 conflicts, and subsequently reused for IPv6 conflicts, due to which this assertion fails.

Checklist

Please read https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/blob/main/CONTRIBUTING.md before opening the merge request. In particular, check that:

• the subject for all commits is concise and explicative
• the message for all commits explains the reason for the change
• the source is properly formatted
• any relevant documentation is up to date
• you have added unit tests if applicable