Limit displayable rows in BluetoothDevicesSlice

The maximum displayable row count in current design is 3.
i.e., There are 1 header and 3 rows in a Slice when the number of
Bluetooth device exceeds 3.

Change-Id: Ie585617da0665dde4cbe1ab60a2693e3e1199c27
Fixes: 121308955
Bug: 114807655
Test: visual, robotests
2 files changed