rilmodem: cancel USSD + minor style fix

Signed-off-by: Jarko Poutiainen <Jarko.Poutiainen@oss.tieto.com>
Merge pull request #80 from ptakalok/master

[rilmodem] Set service class to 0 in call waiting query
Merge pull request #81 from jpoutiai/master

rilmodem: cancel USSD + minor style fix
[rilmodem] Add support for RIL_REQUEST_SCREEN_STATE request

Support for RIL_REQUEST_SCREEN_STATE request will decrease power
consumption as RILD will notify the baseband to suppress certain
notifications (eg. signal strength and changes in LAC/CID, etc.).
Implementation listens to MCE's "display_status_ind" DBus signal for
sending  RIL_REQUEST_SCREEN_STATE.

Signed-off-by: Petri Takalokastari <petri.takalokastari@oss.tieto.com>