MEXICO CITY, July 25 (Reuters) - Mexican drug lord Ismael "El Mayo" Zambada and the son of his former partner, Joaquin "El Chapo" Guzman, were arrested on Thursday in El Paso, Texas, in a major coup for U.S. authorities that may also reshape the Mexican criminal landscape. Zambada is one of the most consequential traffickers in Mexico's history and co-founded the Sinaloa Cartel with El Chapo, who was extradited to the United States in 2017 and is serving a life sentence in a maximum...