Add documentation for RES_OPTIONS.

Related: #1555001

Resolve: BZ #1691552

Now with systemd, this does not work pretty well and users really should
use systemd unit-files for this.

Add option for time saving waiting

Replace date with simple timeout

Rename configurable variable and add documentation

Print log only when didn't reach IP address in time

Add support for IPv6 address

Remove unneeded output

Change -ge to -gt, because equal value is ok

Clarify DNS name option in documentation

  This concept is quite outdated, and not sane to use at all.

  Other references to these files were removed, as well as irrelevant
  info in sysconfig.txt, and some dead code in init.d/functions file.

  Most of these  files were more than 15 years old, making them no
  longer valid or just simply outdated... Files removed:

   * changes.ipv6
   * ipv6-*.howto
   * sysvinitfiles

  Regarding the 'sysvinitfiles' -- the 'initscripts' package is nowadays
  intended for keeping the support for old init scripts still used
  somewhere. However, for creating new services people should use
  systemd now...