FreeBSD needs to cope with multiple version of the zfs_cmd_t
structure. Allowing the platform code to pre and post
process the cmd structure makes it possible to work with
legacy tooling.
Reviewed-by: Jorgen Lundman <lundman@lundman.net>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes#9624