5edb39d032
There are cases where we do not detect the non-viability of a route, but we will instead observe a failure to send. In a Disco path this would normally be handled as a side effect of Disco, which is not available to non-Disco WireGuard nodes. In both cases, recognizing the failure as such will result in faster convergence. Updates #8999 Signed-off-by: James Tucker <james@tailscale.com>