Fix CaptivePortalLoginActivity probes to bypass Private DNS

Test: as follows
    - built
    - flashed
    - booted
    - runtest frameworks-net passes
    - manual testing on captive portal networks
Bug: 64133961
Bug: 77140445
Bug: 78548486

Change-Id: Idbc4d90eeec257b36c5f374d61dea4600a0f8ebb