Testing page: Do not send extraneous setPreferredNetworkType request to system

When the testing page receives the preferred network type from the system,
it calls Spinner.setSelection which calls the OnItemSelectedListener which
in turns call setPreferredNetworkType to the system again.

Due to limitations in Samsung's RIL, this extraneous request will cause
the data to be disconnected when the Testing page is first opened.

Change-Id: I2b60e29d9e9b15e56bd01db5c13546a56503f34a