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.

CRs-Fixed:  564063, 641116
Change-Id: I57c445ee28be4e1c0f2934cb136a70d39447511c