CVE-2024-42135 vhost_task: Handle SIGKILL by flushing work and exiting

In the Linux kernel, the following vulnerability has been resolved: vhosttask: Handle SIGKILL by flushing work and exiting Instead of lingering until the device is closed, this has us handle SIGKILL by: 1. marking the worker as killed so we no longer try to use it with new virtqueues and new flus...