As he prepares to step down from the military’s top post in two weeks, Adm. Mike Mullen braved the bright lights and barbs of The Daily Show on Monday one last time. Mullen, while discussing his career, braced himself for the comedic trap, which host Jon Stewart laid about a  trip they had taken together to Afghanistan in July to visit the troops. Mullen — a veteran of three wars, not to mention countless comedy show appearances — proved his mettle. “I was surprised that when we landed at Kandahar, that you forced them to carry you around on a litter.…