firewall3: Improve ipset support

firewall3: Improve ipset support

This patch is an attempt at improving the ipset support in firewall3.
The following changes have been made:

* The enabled option did not work properly for ipsets, as it was not
checked on create/destroy of a set. After this commit, sets are only
created/destroyed if enabled is set to true.

* Add support for reloading, or recreating, ipsets on firewall reload.
By setting "reload_set" to true, the set will be destroyed and then
re-created when the firewall is reloaded. My use-case for "reload_set"
was to reset sets populated by dnsmasq, without having to restart the
firewall or resort to scripts.

* Add support for the counters and comment extensions. By setting
"counters" or "comment" to true, then counters or comments are added to
the set.

Signed-off-by: Kristian Evensen <kristian.evensen@gmail.com>
re-ordered additional variables
dropped enum OPT_COMMENT & OPT_COUNTERS as unused
implemented exponential delay whilst waiting for ipset deletion/creation
fixed delays made firewall unresponsive for too long on reloads
Signed-off-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>