Check if network has partial connectivity

In some networks, network validation may only get success
result for http probe but fail result for https probe.
For this kind of network, it may still work at some websites
or apps, but user didn't know about that. In order to fix this
issue, we will check if network has partial connectivity and
notify user to make a choice if they want to use this partial
connectivity or not.

Bug: 113450764
Test: 1. Build pass.
      2. Fake partial connectivity case for testing.
      3. atest FrameworksNetTests
      4. atest NetworkStackTests

Change-Id: I69ed00ac4850904ff708c9fef22e148879a10e92