Improve documentation and help text for --route-ipv6.

Signed-off-by: Gert Doering <gert@greenie.muc.de>
Acked-by: David Sommerseth <davids@redhat.com>
Message-Id: 1368873781-29552-1-git-send-email-gert@greenie.muc.de
URL: http://article.gmane.org/gmane.network.openvpn.devel/7598
Signed-off-by: David Sommerseth <davids@redhat.com>