Prop 312: 3.2.7. Publish IPv4 Descriptor on Guessed IPv6 Reachability Failure

Depends on disabling descriptor publication on reachability failures in legacy/trac#33223 (moved).

Should be done after the first IPv6 address guessing feature: legacy/trac#33238 (moved) or legacy/trac#33240 (moved).

If both reachability checks succeed, relays should publish their IPv4 and IPv6 ORPorts in their descriptor.

If only the IPv4 ORPort check succeeds, and the IPv6 address was guessed (rather than being explicitly configured), then relays should:

• publish their IPv4 ORPort in their descriptor,
• stop publishing their IPv6 ORPort in their descriptor, and
• log a notice about the failed IPv6 ORPort reachability check.

See proposal 312, section 3.2.7, Guessed IPv6 Reachability Failure part: https://gitweb.torproject.org/torspec.git/tree/proposals/312-relay-auto-ipv6-addr.txt#n567