Fix geoip by falling back to registered countries.

See 1d2179bc in master for details.

"""
Fall back to registered country if necessary.

When extracting geoip and geoip6 files from MaxMind's GeoLite2 Country
database, we only look at country->iso_code which is the two-character ISO
3166-1 country code of the country where MaxMind believes the end user is
located.

But if MaxMind thinks a range belongs to anonymous proxies, they don't put
anything there.  Hence, we omit those ranges and resolve them all to '??'.
That's not what we want.

What we should do is first try country->iso_code, and if there's no such
key, try registered_country->iso_code which is the country in which the
ISP has registered the IP address.

In short: let's fill all A1 entries with what ARIN et. al think.
"""