Smack: correct behavior in the mmap hook

The mmap policy enforcement was not properly handling the
  interaction between the global and local rule lists.
  Instead of going through one and then the other, which
  missed the important case where a rule specified that
  there should be no access, combine the access limitations
  where there is a rule in each list.

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
Signed-off-by: James Morris <jmorris@namei.org>