Revert "Revert "Telephony: Add getLteOnGsmMode() method (2/2)""

This reverts commit 5a241be6c33290497fe3d2651f9892856df6cb12.
Revert "Revert "Telephony: Add getLteOnGsmMode() method (2/2)""

This reverts commit 77c1f45b1be0a163143b4b931243ed224eed235d.