Add Dual Transfer Mode support.

- In GsmServiceStateTracker, decode the "concurrent services support
indicator" field from RIL_REQUEST_VOICE_REGISTRATION_STATE
request and based on the value of this CSSI field allow concurrent
CS and PS services to applications.

- Notify data connection changed on CSS indicator update.

- When the phone moves from a DTM cell to a non DTM cell while in
active voice call, data connection is not suspended.
To fix this, consider CSS indicator change also for notifying
data connection.

- To determine concurrent voice and data support
we need to query Data Radio Tech

CRs-Fixed:  564063, 641116

Change-Id: I57c445ee28be4e1c0f2934cb136a70d39447511c