audit: Make testing for a valid loginuid explicit.

commit 780a7654 upstream.

audit rule additions containing "-F auid!=4294967295" were failing
with EINVAL because of a regression caused by e1760bd5.

Apparently some userland audit rule sets want to know if loginuid uid
has been set and are using a test for auid != 4294967295 to determine
that.

In practice that is a horrible way to ask if a value has been set,
because it relies on subtle implementation details and will break
every time the uid implementation in the kernel changes.

So add a clean way to test if the audit loginuid has been set, and
silently convert the old idiom to the cleaner and more comprehensible
new idiom.

RGB notes: In upstream, audit_rule_to_entry has been refactored out.
This is patch is already upstream in functionally the same form in
commit 780a7654 .  The decimal constant
was cast to unsigned to quiet GCC 4.6 32-bit architecture warnings.

Reported-By: Steve Grubb <sgrubb@redhat.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Tested-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Eric Paris <eparis@redhat.com>
Backported-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>