ONS: Make PendingIntent IMMUTABLE am: 9bc5a8c2ba am: d56c547aa6 am: 9137cab05f

Original change: https://android-review.googlesource.com/c/platform/packages/services/AlternativeNetworkAccess/+/1566040

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I9b90cf9de2a9efc945551329f298a97d498bfdda