Use two oneway binder interfaces instead.
The interfaces post messages to handlers as was implemented before, but
provide a more strictly defined interface, with less hops between
NetworkAgent, AsyncChannel, and ConnectivityService.
Exempt-From-Owner-Approval: Owners OOO, change approved by team members
Ignore-AOSP-First: merge conflicts in dependent changes
Test: atest FrameworksNetTests CtsNetTestCasesLatestSdk
Change-Id: Ica51d0179bcb3b4e314d2c3e85709aead6ca5657
