Adjusting zvol_immediate_write_sz

[FF]

I couldn't find anything on google doing this with FreeBSD.

Without getting into the reasons for why someone may want to alter the
threshold for varying the way the ZIL interacts with writes. Is there any
obvious reason why creating a boot-tunable or runtime-tunable for this
variable in zvol.c is a bad thing?

Would a set command in the loader already override this without any
additional code otherwise I'm happy to write the code and ask for it to be
committed.

Thanks!

-- 
FF