vhost: Fix livepatch timeouts in vhost_worker()

Livepatch timeouts were reported due to busy vhost_worker() kthreads.
Now that cond_resched() can do livepatch task switching, use
cond_resched() in vhost_worker().  That's the better way to
conditionally call schedule() anyway.

Reported-by: Seth Forshee (DigitalOcean) <sforshee@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Tested-by: Seth Forshee (DigitalOcean) <sforshee@kernel.org>
Link: https://lore.kernel.org/r/509f6ea6fe6505f0a75a66026ba531c765ef922f.1677257135.git.jpoimboe@kernel.org