When a rivalry game happens in the playoffs — all bets are off. That’s the mentality Bear River girls volleyball coach Matt MacDonald has as his No. 2 seed Lady Bruins prepare to host No. 10 seed Colfax in the second round of the Sac-Joaquin Section Division IV playoffs. “When it’s a rivalry, you can throw out the seeds, you can throw out everything,” he said. “We are anticipating a tough game.” The Lady Bruins (26-12, 9-1 Pioneer Valley League) are the 2012 PVL co-champs and are on a five-game winning streak during which they haven’t dropped a set. The …