This modifies the mls constraint for polmatch in the association class.
    Specifically:
    
    - polmatch need no longer make an exception for unlabeled_t
      since a flow will now always match SPD rules with no contexts (per
      the IPSec leak fix patch upstreamed a few weeks back), as
      opposed to needing polmatch access to unlabeled_t.
    
    Signed-off-by: Venkat Yekkirala <vyekkirala@TrustedCS.com>