Fix windows build on older mingw versions.

Add missing #define for IPV6_V6ONLY sockopt.

Fix last remaining fallout of dual-stack patch set in connect() call
for "not CONNECT_NONBLOCK" case.

Signed-off-by: Gert Doering <gert@greenie.muc.de>
Acked-by: Arne Schwabe <arne@rfc2549.org>
Message-Id: <1416257903-24629-1-git-send-email-gert@greenie.muc.de>
URL: http://article.gmane.org/gmane.network.openvpn.devel/9246