Update CTS for getNetworkCountryIso by checking service state

The API returns the ISO-3166-1 alpha-2 country code when attaching
the network. Otherwise, an empty string will be returned.

Bug: 216611016
Test: atest CtsTelephonyTestCases:TelephonyManagerTest#testGetNetworkCountryIso
Change-Id: Iedf38df8f0fd07bc6c32eb70d87920e300812968
1 file changed