Jonah Hill and Channing Tatum, an unlikely duo if there ever was one, basically repeat the same steps of their very funny “21 Jump Street,” and they do it in a way that keeps things fresh while knowingly recycling the same plot. And by knowingly, I mean this film acknowledges what it is, a run-of-the mill sequel, for its entire running time. It’s a self-mocking technique that works well thanks to its stars and the deft comic direction of returning directors Phil Lord and Christopher Miller (Lord and Miller are on a roll, having directed this year’s “The Lego Movie,” as well). This one picks up where the first film left off, with Captain Dickson (Ice Cube in serious comic overdrive) assigning Schmidt (Hill) and Jenko (Tatum) to college. In college they will do exactly what they did undercover in the first movie: Infiltrate the dealers, find the supplier. They get the laughs the same way, through Hill’s self-deprecating, rat-a-tat delivery, and Tatum’s dumb lug shtick. It worked well the first time, and it works well again.