nfs41: pass iomode through layoutreturn args

So that it is possible to return a specific iomode layouts.

Signed-off-by: Peng Tao <tao.peng@primarydata.com>
Signed-off-by: Tom Haynes <Thomas.Haynes@primarydata.com>

include/linux/nfs_xdr.h

@@ -293,6 +293,7 @@ struct nfs4_layoutreturn_args {
 	struct nfs4_sequence_args seq_args;
 	struct pnfs_layout_hdr *layout;
 	struct inode *inode;
+	enum pnfs_iomode iomode;
 	nfs4_stateid stateid;
 	__u32   layout_type;
 };