Default ipv6 configuration does not work

[Greelan]

And I discovered when seeing what ping6 did on my LAN interface that there seems to be an issue where a ULA (Virtual IP) configured on the interface is wrongly used in priority to the GUA configured when pinging an external IPv6 address. I have raised this in a comment in what could be a related issue: https://github.com/opnsense/core/issues/4651#issuecomment-778565211