pNFS: Clear the layout metadata if the server changed the layout stateid

If the server changed the layout stateid's "other" field, then
we should treat the old layout as being completely gone. In that
case, we want to clear the metadata such as scheduled layoutreturns.

Do this by calling pnfs_mark_layout_stateid_invalid().

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