Allow duplicate extents in SMB3 not just SMB3.1.1

Enable duplicate extents (cp --reflink) ioctl for SMB3.0 not just
SMB3.1.1 since have verified that this works to Windows 2016
(REFS) and additional testing done at recent plugfest with
SMB3.0 not just SMB3.1.1  This will also make it easier
for Samba.

Signed-off-by: Steve French <steve.french@primarydata.com>
Reviewed-by: David Disseldorp <ddiss@suse.de>