Update D2D logic in line with new opt-out rules

* Ignore android:fullBackupContent for apps targeting Android S+ while
  in D2D
* Update LocalTransport::getTransportFlags() to support
  FLAG_DEVICE_TO_DEVICE_TRANSFER (required for CTS testing)

Bug: 180523564
Test: atest FullBackupRulesHostSideTest
Change-Id: I115c1c76f4b0d8b486cc9f146ef630fda3ff2a03