NFSv4: Don't request atime/mtime/size if they are delegated to us

If the timestamps and size are delegated to the client, then it is
authoritative w.r.t. their values, so we should not be requesting those
values from the server.
Note that this allows us to optimise away most GETATTR calls if the only
changes to the attributes are the result of read() or write().

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Lance Shelton <lance.shelton@hammerspace.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>