Improve partial connectivity

Improve the design and fix some nits.

Bug: 113450764
Test: 1. Build pass
      2. atest FrameworksNetTests
      3. atest NetworkStackTests
      4. Change captive_portal_https_url to https://invalid.com
      to simulate partial connectivity.
Change-Id: Ia56645841d00d2ed8406cfeacb86a4a27fd58650
2 files changed
tree: b33edc2001df82cd50cc71950bff78ccaf924593
  1. core/
  2. services/
  3. tests/