Our IPv6 Autodiscovery breaks AssumeReachable 1 torrc option

When last changed our IP autodiscovery code and added IPv6 support, we broke AssumeReachable 1

AssumeReachable 1 tells Tor to skip self reachability tests. However, in the latest alpha, a Tor running with this torrc option, if it also has a working IPv6 address that is not configured in any way in torrc (as Address or ORPort) will guess the IPv6 address soon after start:

Guessed our IP address as [public_IPv6_addr] (source: METHOD=INTERFACE).

and immediately trigger self reachability tests including on the IPv4 address:

Now checking whether IPv4 ORPort <public_IPv4_addr>:9001 is reachable... (this may take up to 20 minutes -- look for log messages indicating success)

This has a negative effect, especially on relays or bridges running on localhost / private lan with AssumeReachable 1 and PublishServerDescriptor 0 torrc options.