xenlight: extend type conversion error message with value
xenlight: extend type conversion error message with value

Signed-off-by: Rob Hoes <8783b3376fb07d39edffc8d7da68a6de3874a7e6@citrix.com>

djs55/ocaml-xen-lowlevel-libs,euanh/ocaml-xen-lowlevel-libs,djs55/ocaml-xen-lowlevel-libs,djs55/ocaml-xen-lowlevel-libs,euanh/ocaml-xen-lowlevel-libs,djs55/ocaml-xen-lowlevel-libs,euanh/ocaml-xen-lowlevel-libs