Add External Actions KPI to ipfw(9).

Add External Actions KPI to ipfw(9).

It allows implementing loadable kernel modules with new actions and
without needing to modify kernel headers and ipfw(8). The module
registers its action handler and keyword string, that will be used
as action name. Using generic syntax user can add rules with this
action. Also ipfw(8) can be easily modified to extend basic syntax
for external actions, that become a part base system.
Sample modules will coming soon.

Obtained from:	Yandex LLC
Sponsored by:	Yandex LLC