feat(wireguard): add debug logs for IPv6 detection

- To debug issue #998
- Enable with `LOG_LEVEL=debug`

internal/wireguard/route.go

@@ -19,7 +19,9 @@ func (w *Wireguard) addRoute(link netlink.Link, dst *net.IPNet,
 
 	err = w.netlink.RouteAdd(route)
 	if err != nil {
-		return fmt.Errorf("cannot add route %s: %w", route, err)
+		return fmt.Errorf(
+			"cannot add route for link %s, destination %s and table %d: %w",
+			link.Attrs().Name, dst, firewallMark, err)
 	}
 
 	return err