6d896e1357 ("tools/libxl: Extend datacopier to support reading into a
buffer") changed the semantics of the errnoval parameter for the datacopier
callback without updating all callers. Restore the original behavior for now.
Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>