It is for China to decide what role it plays at the G20 Summit in New Delhi, a top US official has said, asserting that if Beijing wants to come in and be a "spoiler", that option is available to it. US National Security Advisor Sullivan was responding to a question at a White House news conference on Tuesday on the impact of India-China border tensions on the G20 Summit. "As far as the question of tensions between India and China affecting the (G20) summit – really that's up to China. If China wants to come in and play the…