The OutcomeReceiver that gets passed into the EthernetServiceImpl is
hard to use (it is nullable and both onError and onResult can throw
RemoteExceptions).
Note: This is an intermediary state.
The next step will be to completely tear EthernetCallback out of
EthernetNetworkFactory, which will remove a lot of boilerplate code.
Bug: 225317892
Test: atest EthernetManagerTest
Change-Id: Ifc0e1ba29ded933c418e4b335cb731c3496d7e44
251f2fcf13