(Forced commit to list actual problems fixed / PRs affected).

(Forced commit to list actual problems fixed / PRs affected).

Overview of problems fixed:

- fix support for saving and restoring filter/NAT state information
  (across reboots for example);

- ipmon(8) is started before loading any filter/NAT rules;

- ipmon(8) and ipfs(8) do not solely depend on ipfilter_enable anymore,
  they now also work when only ipnat_enable is true;

- the multiple occurrences of code loading the ipfilter kernel module
  have been removed;

- the options have been removed from the _program variables in
  defaults/rc.conf and the comments in that file have been updated to
  reflect (possibly new) reality;

- the rc.conf.5 manual page has been updated to reflect the changes.

Submitted by:	Arjan de Vet <devet@devet.org>
PR:		conf/25223, kern/25344, conf/25809,
		conf/26275, bin/27016, conf/31482