NFS: Prevent 3.0 from crashing if it receives a partial layout

NFS: Prevent 3.0 from crashing if it receives a partial layout

This is a backport of critical parts of
commit 7c24d9489f "NFSv4.1: File layout only supports whole file layouts"

It prevents the file layout driver from (incorrectly) using
partial layouts, but ignores the part of the referenced commmit that
relies on additional machinery to change the LAYOUTGET request
based on layout driver.

Signed-off-by: Fred Isaman <iisaman@netapp.com>
Acked-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>