In order to support constant callers of agent_send_response we add const
specifiers to the its pointer arguments.

Adjust the call tree accordingly.
Signed-off-by: NIra Weiny <ira.weiny@intel.com>
Reviewed-by: NHal Rosenstock <hal@mellanox.com>
Reviewed-by: NJason Gunthorpe <jgunthorpe@obsidianresearch.com>
Signed-off-by: NDoug Ledford <dledford@redhat.com>