Ensure AppPermissionsFragment starts scrolled to the top.

Without this, opening AppPermissionsFragment for an app with many
permissions starts below the header, so it's not visually obvious
which app is open.  This fixes that.

Test: Open AppPermissionsFragment and see header at top.
Test: Open other permissions screens and see they work.
Change-Id: I169e5b02c92b4af031a9d35d22998cf797430a63