nfs41: pull decode_ds_addr from file layout to generic pnfs

It can be reused by flexfile layout.

Reviewed-by: Jeff Layton <jlayton@primarydata.com>
Signed-off-by: Peng Tao <tao.peng@primarydata.com>
Signed-off-by: Tom Haynes <Thomas.Haynes@primarydata.com>
diff --git a/fs/nfs/pnfs.h b/fs/nfs/pnfs.h
index b0168f1..403d7bb 100644
--- a/fs/nfs/pnfs.h
+++ b/fs/nfs/pnfs.h
@@ -312,6 +312,9 @@
 void nfs4_pnfs_ds_put(struct nfs4_pnfs_ds *ds);
 struct nfs4_pnfs_ds *nfs4_pnfs_ds_add(struct list_head *dsaddrs,
 				      gfp_t gfp_flags);
+struct nfs4_pnfs_ds_addr *nfs4_decode_mp_ds_addr(struct net *net,
+						 struct xdr_stream *xdr,
+						 gfp_t gfp_flags);
 
 static inline struct nfs4_deviceid_node *
 nfs4_get_deviceid(struct nfs4_deviceid_node *d)