mac dns: do not run dns-updown in parallel

mac dns: do not run dns-updown in parallel

In case more than one openvpn connection is coming up or going down at
the same time, there is potential for breakage, since the operations
performed are not atomic.

Introduce a locking mechanism, which let's scripts run in sequence, to
prevent races between them.

Change-Id: I7adfaa08df6a17545cca8264d7230b5e65e49719
Signed-off-by: Heiko Hund <heiko@ist.eigentlich.net>
Acked-by: Arne Schwabe <arne-openvpn@rfc2549.org>
Message-Id: <20250711100700.241668-1-frank@lichtenheld.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg32108.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>