ospf6d: fix linkdown handling

ospf6d: fix linkdown handling

Ensure OSPFv3 handles link down even correctly.

OSPFv3 checks only the administrative status of a link instead of its
operative status. This prevents it up from detecting a real link down
event and reacting appropriately. Only protocol timer timeouts make it
detect a link down eventually. This patch makes it look for the operative
status of a link instead of admin status.

Signed-off-by: Dinesh G Dutt <ddutt at cumulusnetworks.com>
Reviewed-by: James Li <jli at cumulusnetworks.com>
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>