Set background app limit to 16

 * For low memory devices, the original limit of 24 would be
   impractical anyways since it cannot contain that many apps.

   (from CAF)

Change-Id: I72ca48cf13183018d3dd2d395a8fc6da45547f81
Allow more background services

 * Some services or broadcast may get tremendous delay because
   of the limited background services. It will bring about many
   issues like alarmmanagerservice's wakelock held too long.

   (from CAF)

Change-Id: Ic4fcd0723bbbbd7a70680be654f784d5ff854a2f