Fix the NFSv4.1/pNFS client return layout on close.

The "return layout on close" case in the pNFS client was badly broken.
Fortunately, extant pNFS servers that I have tested against do not
do this. This patch fixes it. It also changes the way the layout stateid.seqid
is set for LayoutReturn. I think this change is correct w.r.t. the RFC,
but I am not 100% sure.
This was found during recent testing of the pNFS server under development.

MFC after: 2 weeks