To integrate BTstack into Zephyr, please move the BTstack project into the Zephyr root folder 'zephyr'. Please use the Zephry '1.9-branch' for now. In the master branch, Zephyr switched the build system to CMake and this port hasn't been update for that yet.
All examples that provide a GATT Server use the GATT DB in the .gatt file. Therefore you need to run ./update_gatt_db.sh in the example folder after modifying the .gatt file.
This port does not support Data Sources aside from the HCI Controller.