2aa3fbe761 extended zinject_record_t, and in doing so inadvertently
extended zfs_cmd_t, which broke compatibility with userspace tools
without the change.
This fixes that by using some of the unused space in zfs_cmd_t for the
extra fields. We also add an assert to trigger a compile error if the
size ever changes.
Sponsored-by: https://despairlabs.com/sponsor/
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: Rob Norris <robn@despairlabs.com>
Closes#17367
06fa8f3f69