Fix IPv6_V6ONLY logic.

The "ipv6only" setsockopt logic introduced by 8832c6c4cf was inverted,
fix.  Also add a msg() to show what value is set, as that makes strange
v4/v6 connectivity problems much easier to spot.

Signed-off-by: Gert Doering <gert@greenie.muc.de>
Acked-by: Arne Schwabe <arne@rfc2549.org>
Message-Id: <1385847508-32248-1-git-send-email-gert@greenie.muc.de>
URL: http://article.gmane.org/gmane.network.openvpn.devel/8079