Fix testNetworkScanRequestParcel_Parcel CTS

Allow mSpecifiers to be null in case the length of the specifier array
is less than null

Bug: 146363437
Test: Ran CTS

cts-tradefed run cts -m CtsCarrierApiTestCases --test android.carrierapi.cts.NetworkScanApiTest

Change-Id: Iad7d91d8813415bbd2f3b6cad02120e59441e08a