overlay: Enable config_dontPreferApn true

This fixes the issue with prepaid ATT sims not falling over to
correct apn.

Change-Id: I761f8ae0197b9cf64c8166ea520aeaa401525125
Use stock mixer_paths.xml with stock audio.primary

Change-Id: Ia7ca8538408399a9bdb8f60a931a088daef624d9