Currently we create link-local route by creating an always-on IPv6 prefix in the prefix list. This prefix is not tied to the link-local ifa.
This leads to the following problems:
- When flushing interface addresses we skip on-link route, leaving fe80::/64 prefix on the interface w/o any IPv6 addresses.
- When creating and removing link-local alias we lose fe80::/64 prefix
Fix this by attaching ifa to the prefix at the initial creation.