[rilmodem] Implementation for call forwarding activation and deactivation

User can try activate or deactivate the call forwarding from keyboard
instead of registration or erasure. Implementing lacking messages

Signed-off-by: Jussi Kangas <jussi.kangas@oss.tieto.com>
Merge pull request #120 from jkangas/forwarding

Request for pulling call forwarding activate and deactivate support to main branch