Patch to make Route RA IPv6 ready

This little patch makes the Route RA IPv6 ready.

The only missing bit was the status report where "ip route show" will
only output IPv4 routes.
This makes the original RA think that the IPv6 route is always down.

Signed-off-by: Robert Sander <r.sander@heinlein-support.de>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>