Move receiver registration to onPause/onResume for MobileNetworkSettings.

Moving registration and unregistration of receivers on the
MobileNetworkSettings page to the onPause/onResume methods.
Previously this was done in onCreate and onDestroy.
Also, adding null checks in the receivers to ensure that they won't try
to update the UI when the activity is null.

Test: Manual
Bug: 109899326
Change-Id: Id4d6c37d155824b26ee4c3dd33bb6bd8ac7b619b
Merged-In: Id4d6c37d155824b26ee4c3dd33bb6bd8ac7b619b
(cherry picked from commit c3dbff7ccd08a6acb34de9df95424a2d30deaaad)
1 file changed