initialization routines into a ctor, tear-down to a dtor, cleaning
up, etc. This will allow audit records to be allocated from
per-cpu caches.
On recent FreeBSD, dropping the audit_mtx around freeing to UMA is
no longer required (at one point it was possible to acquire Giant
on that path), so a mutex-free thread-local drain is no longer
required.
Obtained from: TrustedBSD Project