audit regressions in 4.11

[Seth Forshee <seth.forshee@canonical.com>]

I've observed audit regressions in 4.11-rc when not using a userspace
audit daemon. The most obvious issue is that audit messages are not
appearing in dmesg anymore. If a sufficient number of audit messages are
generated the kernel will also start invoking the OOM killer.

It looks like previously, when there's no auditd in userspace kauditd
would call kauditd_hold_skb(), which prints the message using printk and
either frees the skb or queues it (with a limit on the number of queued
skb's by default).

Since 5b52330bbfe6 "audit: fix auditd/kernel connection state tracking"
when there's no auditd kauditd will instead use the retry queue, which
has no limit. But it will not process the retry queue when there's no
auditd, so messages pile up there indefinitely.

Thanks,
Seth