NFSv4.1/pnfs: Separate out metadata and data consistency for pNFS

The LAYOUTCOMMIT operation means different things to different layout types.
For blocks and objects, it is both a data and metadata consistency operation.
For files and flexfiles, it is only a metadata consistency operation.

This patch separates out the 2 cases, allowing the files/flexfiles layout
drivers to optimise away the data consistency calls to layoutcommit.

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
diff --git a/fs/nfs/objlayout/objio_osd.c b/fs/nfs/objlayout/objio_osd.c
index 8b5e0e6..5aaed36 100644
--- a/fs/nfs/objlayout/objio_osd.c
+++ b/fs/nfs/objlayout/objio_osd.c
@@ -637,6 +637,8 @@
 	.pg_read_ops             = &objio_pg_read_ops,
 	.pg_write_ops            = &objio_pg_write_ops,
 
+	.sync			 = pnfs_generic_sync,
+
 	.free_deviceid_node	 = objio_free_deviceid_node,
 
 	.encode_layoutcommit	 = objlayout_encode_layoutcommit,