Make sure inform_testing_reachability() reports the correct ports

In legacy/trac#33222 (moved), we added IPv6 ORPort support to inform_testing_reachability(). But that function checks the ORPorts and DirPort itself, rather than logging the reachability checks that were actually launched.

We'd like to pass flags so that it logs the actual reachability tests that are being run. (Rather than re-checking the relay's own routerinfo, which may have changed since the most recent reachability checks were launched.)

But inform_testing_reachability() is called when:

• the first circuit finishes building, or
• tor is reconfigured, and some circuits have already finished building.

So we need to do a bit of a refactor.

The refactor should preserve this behaviour:

• don't log until after the first circuit has finished building (rather than logging as soon as we start building reachability circuits)

And introduce this new behaviour:

• log the ports that were tested recently, rather than the ports that are currently available.

As an alternative, we could move some of the logging into the functions that actually launch the checks. And elevate some of those logs to notice level. (Note that these checks can be launched from at least 4 different locations in tor's code.)