tools/ocaml/xenctrl: Use larger chunksize in domain_getinfolist

tools/ocaml/xenctrl: Use larger chunksize in domain_getinfolist

domain_getinfolist() is quadratic with the number of domains, because of the
behaviour of the underlying hypercall.  Nevertheless, getting domain info in
blocks of 1024 is far more efficient than blocks of 2.

In a scalability testing scenario with ~1000 VMs, a combination of this and
the previous change takes xenopsd's wallclock time in domain_getinfolist()
down from 88% to 0.02%

Signed-off-by: Edwin Török <edvin.torok@citrix.com>
Tested-by: Pau Ruiz Safont <pau.safont@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
(cherry picked from commit 95db09b1b154fb72fad861815ceae1f3fa49fc4e)