Add transport type get function in SimultaenousCallingTracker.java

In checking if two phones support simultaneous call via cellular or WLAN, added getTransportType function in SimultaenousCallingTracker.java. This prevents a NPE that was occuring if IMS phone had not been created when IMS feature was not supported.

Change-Id: Ifebee3b55f5821c180659fa34e8bbef029b9380a
Test: build
Flag: EXEMPT bugfix
Fixes: 390043290