doc: announce parameter change of a service API function

doc: announce parameter change of a service API function

rte_service_attr_get() is passed a uint32_t * to retrieve
an attribute value, this will be changed to uin64_t * as per
patch posted at http://patchwork.dpdk.org/patch/49968/

Signed-off-by: Nikhil Rao <nikhil.rao@intel.com>
Acked-by: Harry van Haaren <harry.van.haaren@intel.com>
Acked-by: Kevin Traynor <ktraynor@redhat.com>
Acked-by: Andrew Rybchenko <arybchenko@solarflare.com>
Acked-by: David Marchand <david.marchand@redhat.com>