Done.
The patch applied, and the module raid6.ko compiled, with no problem.
The machine was rebooted because the crashed raid6.ko would not
unload.
The new raid6.ko loaded and unloaded repeatedly without a problem.
I created a raid6 device with 6 components, and a file system, and it
worked as expected, allowing failure of 1 or 2 component devices, but
not 3.
At present, I have not tried building it into the kernel, and have not
done any hard testing of raid6.