nfsd4: send the special close_stateid in v4.0 replies as well

We already send it for v4.1, but RFC7530 also notes that the stateid in
the close reply is bogus.

Always send the special close stateid, even in v4.0 responses. No client
should put any meaning on it whatsoever. For now, we continue to
increment the stateid value, though that might not be necessary either.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>