pnfs-obj: objlayout_encode_layoutcommit implementation

* Define API for io-engines to report delta_space_used in IOs
* Encode the osd-layout specific information of the layoutcommit
  XDR buffer.

Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
Signed-off-by: Benny Halevy <bhalevy@panasas.com>

fs/nfs/objlayout/objio_osd.c

@@ -1018,6 +1018,7 @@ static struct pnfs_layoutdriver_type objlayout_type = {
 
 	.free_deviceid_node	 = objio_free_deviceid_node,
 
+	.encode_layoutcommit	 = objlayout_encode_layoutcommit,
 	.encode_layoutreturn     = objlayout_encode_layoutreturn,
 };