NFS: Add attribute update barriers to NFS writebacks

Ensure that other operations that race with our write RPC calls
cannot revert the file size updates that were made on the server.

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Tested-by: Chuck Lever <chuck.lever@oracle.com>

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

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

diff --cc fs/nfs/nfs3proc.c
Simple merge

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

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

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

diff --cc include/linux/nfs_fs.h
Simple merge