Add mEnableFailFastRefCounter.

Use a reference counter to control enabling fail fast
as there are now two entities which control failing fast:
ConnectifityService.checkProvisioningUrl and
MobileDataStateTracker.captivePortalCheckComplete.

Bug: 9462512
Change-Id: I0dea0eee519f8ee7f94e79d40e82c18f30d7fe2e