In order to make the next patch more clear, expand may_access() logic.

v2: may_access() returns bool now
Acked-by: NTejun Heo <tj@kernel.org>
Acked-by: NSerge Hallyn <serge.hallyn@canonical.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: NAristeu Rozanski <aris@redhat.com>
Signed-off-by: NTejun Heo <tj@kernel.org>