NFSv4: Fix another bug in the close/open_downgrade code

NFSv4: Fix another bug in the close/open_downgrade code

James Drew reports another bug whereby the NFS client is now sending
an OPEN_DOWNGRADE in a situation where it should really have sent a
CLOSE: the client is opening the file for O_RDWR, but then trying to
do a downgrade to O_RDONLY, which is not allowed by the NFSv4 spec.

Reported-by: James Drews <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Fixes: aee7af356e15 (NFSv4: Fix problems with close in the presence...)
Cc: [email protected] # 2.6.33+
Signed-off-by: Trond Myklebust <[email protected]>