Request cell network after carrier config change

The cell network may reconnect on carrier config change, so a cell
network requested before that may be disconnected after the change.

Only request the cell network after the carrier config change, so the
network connected after the change is used for the test.

Bug: 316154796
Test: atest
Change-Id: Id8cd49ae352fd7899cb45efecd5ccfd760a7b1eb