Merge pull request #78 from jpoutiai/master

provide multi-request support for rilmodem
Merge pull request #79 from jpoutiai/master

rilmodem: fixes possible segfault issue in USSD
rilmodem: cancel USSD + minor style fix

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