Add Windows DNS Leak fix using WFP ('block-outside-dns')

Add Windows DNS Leak fix using WFP ('block-outside-dns')

This option blocks all out-of-tunnel communication on TCP/UDP port 53
(except for OpenVPN itself), preventing DNS Leaks on Windows 8.1 and 10.

The 2.3 version of this patch is only active if compiling for Vista+
(_WIN32_WINNT >= 0x0600) as XP does not have the necessary includes
and libraries.

Reviewed-by: Selva Nair <selva.nair@gmail.com>
Reviewed-by: Lev Stipakov <lstipakov@gmail.com>
Reviewed-by: James Yonan <james@openvpn.net>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <1449780695-3879-1-git-send-email-iam@valdikss.org.ru>
URL: http://article.gmane.org/gmane.network.openvpn.devel/10743

Signed-off-by: Gert Doering <gert@greenie.muc.de>