BRUSSELS (Reuters) - Mastercard Inc's bid for a part of Scandinavian payments group Nets is a significant threat to competition in Europe, the European Commission said on Monday after it was asked by six national competition agencies to examine the deal.The U.S. group announced the deal in August last year to buy three divisions of European rival Nets, covering corporate clearing, instant payments and e-billing.The Commission, which acts as the EU's antitrust enforcer, said it has accepted a..