Check different CellLocation type in GsmDataConnectionTracker

Addressing phone app crash in GsmDataConnectionTracker when CDMALTEPhone
is used. CDMALTEPhone uses CDMA SST so getCellLocation() was returning
an instance of CdmaCellLocation. This was causing a crash when GsmDCT
type casts the instance as GsmCellLocation.

This patch tries to check the instance type before retrieving corresponding
cell id.

Change-Id: I6ac9cd4dc078552dc58d4d9350494a7b608c2b98