Improve the wifi description for the case of private DNS broken

Currently, users don't know if the wifi description shows
"No internet" means it really doesn't have internet access or no
internet is because of private DNS resolution failed. So, Add a
new description for wifi when private DNS is broken.

Bug: 113242081
Test: make -j44 RunSettingsRoboTests \
      ROBOTEST_FILTER=WifiDetailPreferenceControllerTest

Change-Id: I44a7e51cf76dc3f2a6b9583f226af6649f9b1f5f