audit: add a new "type" field to audit_names struct

For now, we just have two possibilities:

UNKNOWN: for a new audit_names record that we don't know anything about yet
NORMAL: for everything else

In later patches, we'll add other types so we can distinguish and update
records created under different circumstances.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>