rados write ops can now return data

This just merged: https://github.com/ceph/ceph/pull/30581 which means that it's possible to construct cls methods that do updates *and* return >0 return codes and (limited) data payload. You need to set the WRITEVEC flag on the rados op for it to work, in order to avoid breaking current users of requests like [stat, write] or [cmpxattr, write], since those guard methods occasionally return data. Enjoy! sage