CVE-2026-43468: net/mlx5: Fix deadlock between devlink lock and esw->wq

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

net/mlx5: Fix deadlock between devlink lock and esw->wq

esw->workqueue executes eswfunctionschangedeventhandler -> eswvfschangedeventhandler and acquires the devlink lock.

.eswitchmodeset (acquires devlink lock in devlinknlpredoit) -> mlx5devlinkeswitchmodeset -> mlx5eswitchdisablelocked -> mlx5eswitcheventhandlerunregister -> flushworkqueue deadlocks when eswvfschangedeventhandler executes.

Fix that by no longer flushing the work to avoid the deadlock, and using a generation counter to keep track of work relevance. This avoids an old handler manipulating an esw that has undergone one or more mode changes: - the counter is incremented in mlx5eswitcheventhandlerunregister. - the counter is read and passed to the ephemeral mlx5hostwork struct. - the work handler takes the devlink lock and bails out if the current generation is different than the one it was scheduled to operate on. - mlx5eswitchcleanup does the final draining before destroying the wq.

No longer flushing the workqueue has the side effect of maybe no longer cancelling pending vportchangehandler work items, but that's ok since those are disabled elsewhere: - mlx5eswitchdisablelocked disables the vport eq notifier. - mlx5eswvportdisable disarms the HW EQ notification and marks vport->enabled under statelock to false to prevent pending vport handler from doing anything. - mlx5eswitchcleanup destroys the workqueue and makes sure all events are disabled/finished.