DO NOT MERGE: Fixed an issue about notification icons on AOD

Previously low priority notifications were hidden
on AOD unconditionally which is wrong.

Bug: 135627468
Test: atest SystemUITests
Merged-in: Ia64238f30620d9906aa50c2469121c2653875e8d
Change-Id: Ia64238f30620d9906aa50c2469121c2653875e8d