Change the validation URL for Chinese SIMs

The default HTTPS and fallback validation URLs are not accessible from
China, so users in China never get a validated network on WiFi with the
default AOSP settings. OEMs selling devices targeting China typically
change the check URLs for that reason.

When the device uses a Chinese SIM card, change the default validation
URLs to URLs accessible accessible from China as of now.

Test: inserted China SIM, WiFi off/on, dumpsys network_stack shows new
      URL used
Bug: 111819230
Change-Id: Ib7f41f470ef1a9c7712f2477ebfab44e915cf1b9