CVE-2026-93279: staging: octeon: add missing tasklet_kill in cvm_oct_tx_shutdown

In the Linux kernel, the following vulnerability has been resolved: staging: octeon: add missing tasklet_kill in cvm_oct_tx_shutdown The TX cleanup tasklet can be scheduled by the watchdog IRQ handler to execute cvm_oct_tx_do_cleanup. There can be a pending tasklet in the queue which might run after the cvm_oct_remove() frees net_device structures, causing a use-after-free in cvm_oct_tx_do_cleanup() as it iterates cvm_oct_device[] which is an array of netdevice pointers. Add tasklet_kill() after free_irq() to ensure the tasklet is no longer scheduled or running before teardown proceeds.