After testing all the 5.15.0 kernels available in the archive, I've found that it broke between versions 5.15.0-82.91 and 5.15.0-83.92.
When running the version 5.15.0-82.91, systemd will create the gre6 tunnel interface but will fail with version 5.15.0-83.92.
After testing all the 5.15.0 kernels available in the archive, I've found that it broke between versions 5.15.0-82.91 and 5.15.0-83.92.
When running the version 5.15.0-82.91, systemd will create the gre6 tunnel interface but will fail with version 5.15.0-83.92.