ZFS expects a copyout of zfs_cmd_t on an ioctl error. Our sys_ioctl()
doesn't copyout in this case.

To solve this issue a new struct zfs_iocparm_t is introduced consisting of:
- zfs_ioctl_version (future backwards compatibility purposes)
- user space pointer to zfs_cmd_t (copyin and copyout)
- size of zfs_cmd_t (verification purposes)

The copyin and copyout of zfs_cmd_t is now done the illumos (vendor) way
what makes porting of new changes easier and ensures correct behavior if
returning an error.

MFC after:	10 days