ad trust: accept subordinate domains of the forest trust root
    
    Commit 8b6d1ab854387840f7526d6d59ddc7102231957f added support for
    subordinate UPN suffixes but missed the case where subordinate UPN is a
    subdomain of the forest root domain and not mentioned in the UPN
    suffixes list.
    
    Correct this situation by applying the same check to the trusted domain
    name as well.
    
    Fixes: https://pagure.io/freeipa/issue/8554
    Signed-off-by: Alexander Bokovoy <abokovoy@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>