libxl__stubdomain_is_linux can take a const pointer, so make the change.
This isn't an issue in-tree, but was found with an OpenXT patch where it
was called with only const libxl_domain_build_info available.
Signed-off-by: Jason Andryuk <jandryuk@gmail.com>
Acked-by: Anthony PERARD <anthony.perard@citrix.com>