x86/ioreq server: correctly handle bogus XEN_DMOP_{,un}map_io_range_to_ioreq_server...

x86/ioreq server: correctly handle bogus XEN_DMOP_{,un}map_io_range_to_ioreq_server arguments

Misbehaving device model can pass incorrect XEN_DMOP_map/
unmap_io_range_to_ioreq_server arguments, namely end < start when
specifying address range. When this happens we hit ASSERT(s <= e) in
rangeset_contains_range()/rangeset_overlaps_range() with debug builds.
Production builds will not trap right away but may misbehave later
while handling such bogus ranges.

This is XSA-238.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>