audit_pid with multiple userspace auditd processes

[Eric Paris]

So I noticed today something strange, but maybe not wrong?

lets say userspace starts 2 copies of auditd.  Then they kill the first
copy.  The kernel at that point thinks there is no userspace auditd
running and will instead send things to dmesg

We could fix it by changing the handling in audit_receive_msg to reject
setting the audit_pid to 0 if the current audit_nlk_pid !=
NETLINK_CB(skb).pid.

It's not a big deal, maybe we just call results of audit with multiple
userspace auditd's running at the same time a undefined and not care.

Anyone think that's worth a patch?

-Eric