refactor struct route_ipv6, bring in line with struct route_ipv4 again

refactor struct route_ipv6, bring in line with struct route_ipv4 again

adjust "struct route_ipv6" (and all users) to reflect changes
to "struct route_ipv4" done in commit 7fb0e07e, namely:

 - new member "r6->flags"
 - "r6->defined"        becomes "r6->flags & RT_DEFINED"
 - "r6->metric_defined" becomes "r6->flags & RT_METRIC_DEFINED"
 - route addition status is stored in "r6->flags & RT_ADDED"

Signed-off-by: Gert Doering <gert@greenie.muc.de>
Acked-by: Arne Schwabe <arne@rfc2549.org>
Message-Id: <1441985627-14822-2-git-send-email-gert@greenie.muc.de>
URL: http://article.gmane.org/gmane.network.openvpn.devel/10083