Only apply flag when it has been changed

The properies object provided in onPropertiesChanged only contains
flag(s) that have been added/deleted/updated, changing an unrelated flag
in the same namespace will trigger onPropertiesChanged to be executed
and the properties object won't have your flag, even though it mighet be
set in deviceconfig.

Test: It builds
Bug: 144693310
Change-Id: Iae1692456266efb860f875f3df33fee5831f60cd