location-importer: Fix Spamhaus ASN-DROP parsing

location-importer: Fix Spamhaus ASN-DROP parsing

The format of this list has changed, from a plain text file with a
customer schema to JSON. Adjust our routines accordingly to make use of
this list again.

The second version of this patch incorporates Michael's feedback on the
first version, and adds AS names to the autnums table in case they are
not there already, which closes some gaps on rogue ASNs in the LACNIC
area.

Signed-off-by: Peter Müller <peter.mueller@ipfire.org>
Tested-by: Peter Müller <peter.mueller@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>