Update code to refresh the default voice sub from Telecom.

Ensure the change is only applied when there actually is a change to be
made.  Also ensure that setting the default to "ask every time" is
propagated as well.

Test: Manual
Bug: 128916238
Change-Id: Ic4995808ddd393a89f1340bdf84ad2b0a4904d6d
1 file changed