Refactored setCurrentFunction and setUsbDataUnlocked into single method.

This gets rid of an extraneous configuration change when going from
adb to adb + file transfer as previously the config would have been
reset once for functions and once for data unlocked.

It also simplifies some of the code.

Test: manually changing usb configurations
Change-Id: Ica10a195338b2189db13113f44657393db110bee