s3/smbd: redesign macOS copyfile copy-chunk

s3/smbd: redesign macOS copyfile copy-chunk

The copy-chunk request chunk_count can be 0 and Windows server just
returns success saying number of copied chunks is 0.

macOS client overload this after negotiating AAPL via their SMB2
extensions, meaning it's a so called copyfile request (copy whole file
and all streams).

We previously checked this at the SMB layer, with this patch we just
send this down the VFS, if vfs_fruit is loaded it implements the macOS
copyile semantics, otherwise we get Windows behavour..

No change in behaviour.

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Stefan Metzmacher <metze@samba.org>