vNUMA: validate XEN_DOMCTL_setvnumainfo input

vNUMA: validate XEN_DOMCTL_setvnumainfo input

As we get ready to use the information set for a domain here we should
make sure it is actually valid: Both vNode and pNode numbers should be
in range. Do a little bit of other cleanup so the code ends up looking
reasonably consistent in style.

Along with this goes that we don't need an array of unsigned int to
store the pNode number - a nodeid_t one (a quarter the size) suffices.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Ian Campbell <ian.campbell@cigtrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>