“On the question of whether Advanta owed a duty of care as manufacturer to the applicant farmers, the Court of Appeal erred in proceeding on the basis that the potential for the farmers to avail themselves of contractual and statutory protection in their dealings with distributors, and the absence of statutory protection of the farmers as consumers in Commonwealth consumer protection legislation, were matters which supported not expanding the protection available to persons in the position of the applicant farmers by recognising a duty of care.”