This frame grab from video, provided by the Mexican government, shows Ovidio Guzman Lopez being detained in Culiacan, Mexico, Oct. 17, 2019. (AP) MEXICO CITY — With Sinaloa cartel boss Joaquín “El Chapo” Guzmán serving a life sentence, his sons steered the family business into fentanyl, establishing a network of labs churning out massive quantities of the cheap, deadly drug that they smuggled into the U.S., prosecutors revealed in a recent indictment. Although Guzmán’s trial revolved around cocaine shipments, the case against his sons exposes the inner workings of a cartel undergoing a generational shift as it worked “to manufacture…