Add documentation for CaptivePortal APP_RETURN_*

This fixes API review requests.

Test: atest FrameworksNetTests NetworkStackTests
Bug: 126883311
Change-Id: I0632a98675e65c5e722e81a2c1e0cf1403b54395
1 file changed
tree: c78b86db44d91fafcab956c0b249f00738972d48
  1. core/
  2. services/
  3. tests/