script-options.rst: Update ifconfig_* variables

script-options.rst: Update ifconfig_* variables

- Remove obsolete ifconfig_broadcast. Since this was
  removed in 2.5.0, do not add a removal note but just
  completely remove it.
- Add missing documentation of IPv6 variants for
  ifconfig_pool_* variables.

Github: fixes Openvpn/openvpn#527
Change-Id: Ia8c8de6799f0291fc900628fbd06c8a414e741ca
Signed-off-by: Frank Lichtenheld <frank@lichtenheld.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20240321161623.2794161-1-frank@lichtenheld.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg28438.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit a94226cdc8ed037a6763675aa47e6c821983f174)