Police are investigating a second anti-white bias incident in Brooklyn where the attacker called his victim "cracka," the Daily News has learned. A 51-year-old white man told cops he was on Nostrand Ave. near Glenwood Road in East Flatbush when a black man ran up and knocked him to the ground about 5:40 p.m. Monday. "This is for Malcolm X, cracka," the brute said before storming off