rules.pl: Add tiny ipset_restore function.

rules.pl: Add tiny ipset_restore function.

This helper function is used to load a previously exported list of
networks for a given country code into the ipset module, so it can be
used for any kind of firewall rules.

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