[CIFS] Set copychunk defaults

Patch 2 of the copy chunk series (the final patch will
use these to handle copies of files larger than the chunk size.

We set the same defaults that Windows and Samba expect for
CopyChunk.

Signed-off-by: Steve French <smfrench@gmail.com>
Reviewed-by: David Disseldorp <ddiss@samba.org>