Modes dialog fits 3.5 tiles by default

Note that this only works for the default font size/density
configuration, it doesn't guarantee 3.5 tiles being visible in other
configurations.

The purpose is to make it more obvious that the list is scrollable.

Flag: android.app.modes_ui
Test: manually check that the height changed
Bug: 376450983
Change-Id: Ia79dd083e137df546fc915289945b791c8ac7414