CVE-2025-38177 sch_hfsc: make hfsc_qlen_notify() idempotent

In the Linux kernel, the following vulnerability has been resolved: schhfsc: make hfscqlennotify idempotent hfscqlennotify is not idempotent either and not friendly to its callers, like fqcodeldequeue. Let's make it idempotent to ease qdisctreereducebacklog callers' life: 1. updatevf decreases...