tun.c: enclose DNS domain in single quotes in WMIC call

tun.c: enclose DNS domain in single quotes in WMIC call

This is needed to support domains with hyphens.

Not using double quotes here, since our code replaces
them with underbars (see
https://github.com/OpenVPN/openvpn/blob/master/src/openvpn/win32.c#L980).

Github: fixes OpenVPN/openvpn#363

Change-Id: Iab536922d0731635cef529b5caf542f637b8d491
Signed-off-by: Lev Stipakov <lev@openvpn.net>
Acked-by: Selva Nair <selva.nair@gmail.com>
Message-Id: <20230710112122.576-1-lstipakov@gmail.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg26841.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit 4057814a8a783d4fb1475f49f073f6b3a7797677)