Include check on polpermissive relcache for policies

Include check on polpermissive relcache for policies

equalPolicy() is used in the relation cache to check if two policy
definitions are equivalent, but missed to check for polpermissive.

ALTER POLICY cannot switch a policy to be PERMISSIVE or RESTRICTIVE, so
this would need a dropped and then re-created policy, which would
trigger a relcache invalidation.  Anyway, there is no harm in being
consistent in the check, and if one decides to add an ALTER POLICY to
switch PERMISSIVE or RESTRICTIVE, we would be silently in trouble.

Author: Andreas Lind <andreaslindpetersen@gmail.com>
Reviewed-by: Laurenz Albe <laurenz.albe@cybertec.at>
Discussion: https://postgr.es/m/CAMxA3rv1CS6R7JR5ojz-3CmCEnZEFrqu+XXTnGbLRWrjJRH7sA@mail.gmail.com
Backpatch-through: 14