Fix from Bruce Evans. There were missing sets of parantheses:

Fix from Bruce Evans. There were missing sets of parantheses:

1. The checks for the standard data selectors were botched, so %ss == 0
   and probably %cs == 0 were allowed.  A fix is enclosed.  The checks
   for the standard selectors could be omitted without losing anything
   since the standard selectors pass the valid_ldt_sel() tests.