ceph/ceph — pull request #2794 by ketor (2014-10-24 16:05:11+00:00)
Title: librados: remove unneeded callback in librados::IoCtxImpl::aio_operate

There is no need to call the on_ack callback if the request does not requir for it.
In our practice, after this patch applied the rbd_write latency descreased avg 4us.

Signed-off-by: Ketor Meng