Pre-P target SDK can't silence alarms/media in dnd

In P, users can toggle alarms and media to bypass priority
mode DND.  As a result, apps targetting pre-P, will not be able to
silence alarms or media (cannot disallow alarms/media from bypassing
DND).

Bug: 70662324
Test: make cts-verifier -j40, Notification Attention Management Test
Change-Id: I3d97530bfd2009863c69aa6adfc706551633fcff