AUDIT: buffer audit msgs directly to skb

Drop the use of a tmp buffer in the audit_buffer, and just buffer
directly to the skb.  All header data that was temporarily stored in
the audit_buffer can now be stored directly in the netlink header in
the skb.  Resize skb as needed.  This eliminates the extra copy (and
the audit_log_move function which was responsible for copying).

Signed-off-by: Chris Wright <chrisw@osdl.org>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>