SMB3: GUIDs should be constructed as random but valid uuids

GUIDs although random, and 16 bytes, need to be generated as
proper uuids.

Signed-off-by: Steve French <steve.french@primarydata.com>
Reviewed-by: Aurelien Aptel <aaptel@suse.com>
Reported-by: David Goebels <davidgoe@microsoft.com>
CC: Stable <stable@vger.kernel.org>