libxc: Introduce xc_domain_setvnuma to set vNUMA

libxc: Introduce xc_domain_setvnuma to set vNUMA

With the introduction of the XEN_DOMCTL_setvnumainfo
in patch titled: "xen: vnuma topology and subop hypercalls"
we put in the plumbing here to use from the toolstack. The user
is allowed to call this multiple times if they wish so.
It will error out if the nr_vnodes or nr_vcpus is zero.

Signed-off-by: Elena Ufimtseva <ufimtseva@gmail.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>