only enable radv if upstream connection available

[Stefan Hellermann]

Hi,

is it possible to only announce IPv6 RA if you receive a default route
via another protocol in bird?
like the following:


Upstream IPv6 Router
Runs OSPF3, announce ::/0 to link1 + link2

^
II

link1 + link2 parallel to downstream router

II
v

Downstream IPv6 Router, runs bird
Runs OSPF3, announce local net to upstream router on link1 + link2
additionally annouce IPv6 RA to clients if ::/0 from upstream received

^
II
local net to clients, only use IPv6 if connection to upstream router is ok.