Freeze networkstack-aidl-interfaces to version 19 and use it

1. Run `m networkstack-aidl-interfaces-freeze-api`.
2. Remove the code "frozen: true" in Android.bp.
3. Update networkstack-aidl-latest to use NetworkStack v19.

Bug: 240259333
Bug: 261404136
Test: atest NetworkStackTests
Change-Id: If90cfc08e655710767c9c92b0e449b7febc1c0df
29 files changed