How can I force esp-idf to use sdkconfig.defaults.c6_thread for Thread building? (CON-1343)

[lboue]

Describe the bug I am trying to build the Multiple On Off plugin unit example for Thread but it build for Matter over WiFi.

By default it loads sdkconfig.defaults.esp32c6. How can I force esp-idf to use sdkconfig.defaults.c6_thread?

Environment

• ESP-Matter Commit Id: 131c1ae7f787c24d103459efa62d486c3d045936

• ESP-IDF Commit Id: 3b8741b172dc951e18509698dee938304bcf1523

• SoC (eg: ESP32 or ESP32-C3):

• Device Logs (Please attach the log file):

• Host Machine OS: Ubuntu 22.04.5 LTS

• Host Machine Python version :Python 3.10.12

• Commissioner app and versions if present: N/A

• Home hub app and versions if present: N/A

• Commissioner's logs if present: N/A

Any additional details

cd ~/esp-matter/examples/multiple_on_off_plugin_units
idf.py set-target esp32c6
idf.py menuconfig