Thirty-five years after she straddled an enemy cannon in defiance of the United States' involvement in the Vietnam War, Jane Fonda has vets in a frenzy about a visit to Palm Beach for a fund-raiser next week. Some of the 7,000-plus members of the American Legion in Palm Beach, Martin and Okeechobee counties were expecting to be called to picket Tuesday's luncheon of the YWCA at The Breakers. The silver-screen legend is scheduled to speak before 300-plus, who plunked down 300 bucks each for the Y's shelter for battered women, Harmony House. Cops and hotel honchos were preparing. But just...