vdev props comment and manpage should include zfsd and FreeBSD mentions

Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Rob Norris <robn@despairlabs.com>
Reviewed-by: Allan Jude <allan@klarasystems.com>
Signed-off-by: Alek Pinchuk <apinchuk@axcient.com>
Closes #15968