When activity is recreated, fragments are automatically reattached.
Need to check the savedInstanceState is null or not when we want to add framgment in MobileNetworkActivity.
(lost to check in ag/9667137)
Bug: 154087690
Test: Manual
make RunSettingsRoboTests -j ROBOTEST_FILTER=MobileNetworkActivityTest
Change-Id: Id169353f6dc10306dddd823a904f0803b26a6ddc