libxl: tooling expects wrong errno

libxl: tooling expects wrong errno

When iommu is not enabled for a given domain then pci passthrough
hypercalls such as xc_test_assign_device return EOPNOTSUPP.
The code responsible for this is in "iommu_do_domctl" inside
xen/drivers/passthrough/iommu.c
This patch fixes the error message reported by libxl when assigning
pci devices to domains without iommu.

Signed-off-by: Grzegorz Uriasz <gorbak25@gmail.com>
Tested-by: Grzegorz Uriasz <gorbak25@gmail.com>
Backport: 4.13
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Release-acked-by: Paul Durrant <paul@xen.org>