dns: also (re)place foreign dhcp options in env

dns: also (re)place foreign dhcp options in env

Override DNS related foreign_options with values set by the --dns
option. This is done so that scripts looking for these options continue
to work if only --dns option were pushed, or the values in the
--dhcp-options differ from what's pushed in --dns.

Signed-off-by: Heiko Hund <heiko@ist.eigentlich.net>
Acked-by: Frank Lichtenheld <frank@lichtenheld.com>
Message-Id: <20220527012457.1819262-5-heiko@ist.eigentlich.net>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg24432.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>