Telephony: Add option for using regular poll state for airplane mode

The modemTriggeredPollState breaks airplane mode on some devices.
Although the UI shows that airplane mode is activated, the fact is that
the radio remains active and in service. By using regular pollState()
here, service state in sim status shows correctly radio off.

Enable with setting prop:
ro.telephony.ril.config=legacypollstate

Test: Insert SIM card. Put device into airplane mode. Go into
SIM Status and verify that it says "Radio off".

Change-Id: If2ab5b088a13b1a159e01f82fbea1f58a77b64cd