floss: Fix bluetooth_packetgen include

Should be migrated to system/gd as well. Not doing so caused
BluetoothGeneratedPackets_rust to be always rebuilt since we don't
detect the right output file.

Bug: 205591223
Tag: #floss
Test: Build on Linux

Change-Id: Ife2b03e993a2d5e952f483eda264494c386a7362