Merge "Change the doc to reflect the default status of preferential network service" into sc-dev am: c03fb15e29 am: c45b4a0a53

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/15329706

Change-Id: Ie3d47fc503b206c56349394905f9849ad8cdb11b