[rilmodem] unregister unsolicited message

Signed-off-by: Jarko Poutiainen <Jarko.Poutiainen@oss.tieto.com>
[rilmodem] fix group queue cleanup

Signed-off-by: Jarko Poutiainen <Jarko.Poutiainen@oss.tieto.com>
Merge pull request #104 from jpoutiai/master

driver clean up fixes.