GPO: Close group policy file after copying
    
    The SMB protocol sequence for copying the content of group policy files
    should be:
    - smbc_getFunctionOpen()
    - smbc_getFunctionRead()
    - smbc_getFunctionClose().
    
    Inform the AD server, that we do not need further access to a policy file
    after we have copied its content.
    
    Resolves:
    https://pagure.io/SSSD/sssd/issue/3324
    
    Signed-off-by: REIM THOMAS <reimth@gmail.com>
    
    Reviewed-by: Pawel Polawski <ppolawsk@redhat.com>
    Reviewed-by: Sumit Bose <sbose@redhat.com>