dhcp6: delay at least 10s before attempts

Otherwise we might exceed fiber7’s firewall rules and get blacklisted.

cmd/dhcp6/dhcp6.go

@@ -55,6 +55,7 @@ func logic() error {
 	for c.ObtainOrRenew() {
 		if err := c.Err(); err != nil {
 			log.Printf("Temporary error: %v", err)
+			time.Sleep(10 * time.Second)
 			continue
 		}
 		log.Printf("lease: %+v", c.Config())