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. Entering the PIN before for modems that already support that feature is innocuous, so we enter the PIN from ofono in all cases.

This fixes

https://bugs.launchpad.net/ubuntu/+source/ubuntu-system-settings/+bug/1375945

Tested in

system-image-cli -i
current build number: 263
device name: mako
channel: ubuntu-touch/utopic-proposed
last update: 2014-09-30 07:59:46
version version: 263
version ubuntu: 20140930
version device: 20140929.1
version custom: mako-0.6

system-image-cli -i
current build number: 78
device name: krillin
channel: ubuntu-touch/ubuntu-rtm/14.09-proposed
last update: 2014-10-02 15:08:43
version version: 78
version ubuntu: 20141002
version device: 20141002-d5938d7
version custom: 1411735617

ril_pin_send() implements ofono_sim_driver.send_passwd(). Looking at the sim core code, this function is called when DBus method EnterPin() is called. This method is invoked with the current value of PinRequired as "type" argument (see doc/sim-api.txt), which is usually "pin", but could be "pin2" or others. So in case we implement in the future things like FDN, that use pin2, we will have to check the current pending pin here to use either RIL_REQUEST_ENTER_SIM_PIN or RIL_REQUEST_ENTER_SIM_PIN2, for instance.

Note that when PinRequired is "puk" we use ResetPin instead, and this function is not called.