SystemUI: Update carrier label margin right after setting the padding

This change addresses the two following issues:

* When restarting SystemUI using `pkill -9 systemui`, carrier label's
  margin start would not get initialized since onConfigurationChanged()
  didn't get called.

* onConfigurationChanged() was being called before onApplyWindowInsets()
  resulting in invalid mPadding.first being used.

Change-Id: I076d1e9cd7a2a011512f5dbd5de4a9a991f28042