MILAN — As of Wednesday evening, Brock Nelson still had some pretty important homework to do. His uncle, Dave Christian — a member of the 1980 U.S. Olympic Miracle on Ice team — was on his way to Milan to watch his nephew in the Olympics. Nelson still hadn’t watched the new Netflix documentary memorializing the team , in which Christian played a prominent role. “It’s on my to-do list today,” Nelson told The Post after Team USA practiced. “I’ve heard really good things. I’ve heard it’s pretty