rilmodem: Enter PIN before unlocking it

We enter the SIM PIN in case it has not been entered yet when unlocking
the PIN. This homogenizes the unlock feature for different modems, as
in some cases the modem firmware already enters the PIN before
unlocking but in other cases it does not.
Merge pull request #127 from alfonsosanchezbeato/enter-pin-on-unlock

Enter PIN before unlocking it