vfs: add parameter to copy chunk VFS function to handle dup_extents

vfs: add parameter to copy chunk VFS function to handle dup_extents

FSCTL_DUPLICATE_EXTENTS_TO_FILE must be handled as a COW clone. Add a
copy-chunk flags parameter to the VFS to handle this.

Signed-off-by: Aurelien Aptel <aaptel@suse.com>
Signed-off-by: David Disseldorp <ddiss@samba.org>
Reviewed-by: Ralph Böhme <slow@samba.org>