Check ServiceState when showing dialog

When showing the dialog the first time cellular data is turned off from
QS, check if the data network is in service. If it's not, do not believe
the carrier name and use a generic string instead.

Test: atest NetworkControllerDataTest
Bug: 156238588
Change-Id: Iee8091921ecdaba0c18f67080348240b8b8f67a7