pnfs: write: Set mds_offset in the generic layer - it is needed by all LDs

In current pnfs tree, all the layouts set mds_offset in their
.write_pagelist member.
mds_offset is only used by generic layer and should be handled by it.

This patch is for upstream. It is needed in this -rc series to fix a
bug in objects layout_commit.

I'll send patches for objects and blocks to be
squashed into current pnfs tree.

TODO: It looks like the read path needs the same patch.

Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index e268e3b..7271680 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -864,6 +864,8 @@
 
 	data->args.fh     = NFS_FH(inode);
 	data->args.offset = req_offset(req) + offset;
+	/* pnfs_set_layoutcommit needs this */
+	data->mds_offset = data->args.offset;
 	data->args.pgbase = req->wb_pgbase + offset;
 	data->args.pages  = data->pagevec;
 	data->args.count  = count;