rules.pl: Refactor logic to handle the IP blocklist feature.

rules.pl: Refactor logic to handle the IP blocklist feature.

* Fixes that the same chain would be created each time a firewall
reload is performed.

* Also fixes multiple log and drop rules inside the the BLOCKLIST_DROP
  chains after doing a firewall reload.

* Orphaned BLOCKLIST_DROP chains now will be flushed and removed in case
  the blocklist gets disabled or the entire feature will be swithed off.

Signed-off-by: Stefan Schantl <stefan.schantl@ipfire.org>