TCM devotes its schedule tonight to movies about, and set in, Vietnam, and the evening ends with two films that represent the opposite ends of the political spectrum during those divisive years. First, from 1968, is The Green Berets, co-directed by and starring John Wayne, who plays a colonel leading his Green Berets on a pair of high-risk missions. Listen for the title song, sung by Barry Sadler, which personifies the jingoistic, America-first tone of this movie. Jim Hutton, David Janssen co-st