Adjusting zvol_immediate_write_sz

[Steven Hartland]

I don't see why not FF, if you would like to throw us a quick patch then 
I'd be happy to review and commit.

On 22/10/2015 23:31, FF wrote:
> 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!
>