xen: update vscsiif.h

Update include/xen/interface/io/vscsiif.h to its newest version.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Link: https://lore.kernel.org/r/20220428075323.12853-2-jgross@suse.com


Signed-off-by: Juergen Gross <jgross@suse.com>