Needless to say, Khan’s got a firm grip on his fans. With “Sultan, ” the latest offering from producing/distributing juggernaut Yash Raj Films, director Ali Abbas Zafar seems to want to tighten that hold still further. The story of a once-decorated wrestler, whose glory days come to a screeching halt when personal tragedy strips his will to fight, “Sultan” presents Khan(in the title role) in that classic underdog sports movie that should charm just about all of us. But as the film inches along its bloated 170-minute runtime, Zafar, Sultan, and Khan’s grasps each begin to slip.