Better notification to user when DNS-over-TLS is broken

Provide a specifc notification to let users know that device
has no internet is because it really doesn't have internet access
or it's caused by private DNS resolution failed.

Bug: 113242081
Test: atest FrameworksNetTests
Change-Id: I710c88a4742f5fd56c39fc797d7fa3ad36dba553
12 files changed