[rilmodem][WIP] removing need for setting modem online from dbus API

If there is no set_online method implemented in driver, sim_state_watch
in core sets modem online automatically. If there is one, it does not
do that. Removing online method to enable smooth online going.

Signed-off-by: Jussi Kangas <jussi.kangas@oss.tieto.com>
Merge pull request #36 from jkangas/master

Request for pulling fix for not going online without request issue in main branch