NFSv4: Use the open stateid if the delegation has the wrong mode

Fix nfs4_select_rw_stateid() so that it chooses the open stateid
(or an all-zero stateid) if the delegation does not match the selected
read/write mode.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

diff --cc fs/nfs/nfs4_fs.h
Simple merge

diff --cc fs/nfs/nfs4proc.c
Simple merge

diff --cc fs/nfs/nfs4state.c
Simple merge