[rilmodem] define SERVICE_CLASS_NONE

Signed-off-by: Jarko Poutiainen <Jarko.Poutiainen@oss.tieto.com>
[rilmodem] use SERVICE_CLASS_NONE insteead of hard coded value

Signed-off-by: Jarko Poutiainen <Jarko.Poutiainen@oss.tieto.com>