location-functions.pl: Recognise XD / LOC_NETWORK_FLAG_DROP

location-functions.pl: Recognise XD / LOC_NETWORK_FLAG_DROP

This enables creating firewall rules using the special country code "XD"
for hostile networks safe to drop and ipinfo.cgi to display a meaningful
text for IP addresses having this flag set.

At the moment, the "LOC_NETWORK_FLAG_DROP" is not yet populated, but
will be in the future (as soon as libloc 0.9.9 is released and running
in production).

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