Fix avoidBadWifi behavior with IPv6 provisioning

IPv6 provisioning loss should be ignored when avoidBadWifi is false, not
true.

Bug: 139023420
Test: with avoidBadWifi=false, when connected to a mobile hotspot that
      loses connectivity, WiFi does not disconnect anymore

Change-Id: I534df1595a123866df9ba9f6429331e7fb1c5251