A friend of the alleged neo-Nazi who smashed a U-Haul box truck into the White House security barrier and allegedly told the FBI he wanted to kill the president told The Post he’s worried about his state of mind. The former classmate, who attended school with Sai Varshith Kandula, 19, said: “I feel like something … either has gone badly internally inside him or maybe between the family.” Kandula — who emerged from the rented truck with a Nazi flag after his unsucessful attempt to reach the White House — was “the quiet kid” who enjoyed tennis, according to Aniket...