For back to back setPreferredDataCall, send failure on first callback.

If setPreferredDataSubscriptionId call is received while Telephony is
validating another subscription, we'll always stop previous validation
and failure will be sent to previous callback. Then we'll process the
new request.

Bug: 137297807
Test: unittest
Change-Id: Ib82d26ee7fc9cbc3bb2ce3e1ca46f5f1d17db7d8
Merged-In: Ib82d26ee7fc9cbc3bb2ce3e1ca46f5f1d17db7d8