Correct a typo to fix chown(2).  It was broken since r274476.

Pointy hat to:	kib
X-MFC-With:	r274476
Migrate the callouts from using mutex locks to being mpsafe with
the locks being held by the callers.

Kill callout_drain() and use callout_stop().
Merge remote-tracking branch 'freebsd/master' into hardened/current/master