x/sys/unix/linux: update Linux to v6.6

[mauri870]

The Linux kernel v6.6 released today, 30 October 2023.

https://www.kernel.org

We should be able to update the sources in x/sys by changing the unix/linux/Dockerfile and running GOOS=linux ./mkall.sh. This should be done for all architectures.

[gopherbot]

Change https://go.dev/cl/538378 mentions this issue: unix/linux: update Linux kernel to v6.6

[tklauser]

We usually don't require issues for these types of updates in x/sys. It's fine to just open a CL.