radv/ci: reboot the DUTs when hitting a ring timeout

I am not super happy about doing this, as this means we will potentially be introducing regressions because CI would have papered over a rare race condition... But the situation is that this is already happening, and improving the reliability will likely come from tracking the occurence rate of hangs in an external system.

Signed-off-by: Martin Roukala (né Peres) martin.roukala@mupuf.org