iommufd: Reject non-zero data_type if no data_len is provided

Since the current design doesn't forward the data_type to the driver to
check unless there is a data_len/uptr for a driver specific struct we
should check and ensure that data_type is 0 if data_len is 0. Otherwise
any value is permitted.

Fixes: bd529dbb ("iommufd: Add a nested HW pagetable object")
Link: https://lore.kernel.org/r/0-v1-9b1ea6869554+110c60-iommufd_ck_data_type_jgg@nvidia.com


Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>