Lex the police dog from central Illinois is far from top dog in drug-sniffing skills.That’s the core finding of a potentially influential new ruling from the 7th U.S. Circuit Court of Appeals, which considered the question of how much police should rely on their K-9 partners to justify searches when a dog’s own competence, as in Lex’s case, is itself suspect.The opinion stems from an appeal by Larry Bentley Jr, a St. Louis man serving 20 years in prison for drug possession. He argued the 20 kilograms of cocaine Bloomington …