CVE-2026-98953: devlink: fix devlink_rel reference leak when notify work is pending

In the Linux kernel, the following vulnerability has been resolved:

devlink: fix devlinkrel reference leak when notify work is pending

devlinkrelnestedinnotifyworkschedule() takes a reference on the devlinkrel for the notify work and then queues the work, ignoring the return value of scheduledelayedwork(). If the work is already pending, nothing new is queued, the work runs only once and drops only one reference, so the extra one is leaked together with the devlinkrel and its index in devlinkrels.

This is easy to hit. devlregister() of a nested instance queues the work, and if the instance is unregistered before the work has run, devlinkrelput() queues it again while it is still pending. The work also keeps rescheduling itself for as long as the parent devlink lock cannot be taken, which widens the window. Registering and unregistering a nested devlink instance 100 times while holding the parent lock leaks all 100 devlinkrel objects.

The reschedule path in devlinkrelnestedinnotifywork() has the same problem: if the work was queued again while it was running, the reference it holds is never dropped.

Drop the reference in both places when the work was already pending. The pending work holds its own reference, so this can not be the last one.