Fix maxvalue in DNS plugin
    
    Having a Parameter maxvalue larger that 2G makes Python convert it
    to "long" type instead of "int" type. Our framework than fails to
    bootstrap the API when it detects long integer in Parameter
    maxvalue.
    
    Remove the clashing maxvalue out entirely as we can't transfer
    values larger than 2G anyway (xmlrpc limitation).
    
    https://fedorahosted.org/freeipa/ticket/2082