NFSv4.1/pNFS: pnfs_mark_matching_lsegs_return must notify of layout return

It's not sufficient to just mark the layout segment for layout return. We
also need to set the NFS_LAYOUT_RETURN_BEFORE_CLOSE flag in the layout header.

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>