gptzfsboot grew a lot after skein support was added; need knob to control bloat

[Ngie Cooper]

On Sat, Jan 28, 2017 at 12:21 PM, Allan Jude <allanjude at freebsd.org> wrote:

...

> The 'zfsboot' version, is dd's into the zfs boot code area. It is read
> by the assembly code there. It is important the file be the size that
> will be read, so it is padded out. That file is currently only used for
> MBR booting from ZFS.

Thank you for the info -- it would be really nice if this was noted in
the Makefile in more detail for the next soul who wonders why the
sizes are so different.
Thanks!
-Ngie