Fixes min priority notifications in shelf.

This change fixes an issue where min priority notifications were no
longer appearing in the notification shelf, leading to display glitches
while scrolling the notification shade.  ag/5220056 incorrectly inlined
the constant NotificationShelf.SHOW_AMBIENT_ICONS as false in two places
instead of true, which caused the issue.

Bug: 111405682
Test: manually
Change-Id: I5dbbdc2749b31464838ec9b9b4e04a4de687af12