Goo Goo Dolls guitarist and singer John Rzeznik declared that Sunday night's show with modern rockers Tonic at the Allentown Fair was "like a regular rock concert," and indeed it was. But it was an equal rockertunity event, where boomers jammed with teens, who grooved with their parents and little brothers and sisters.The Goo Goos offered something to please all ages: a tatooed lead singer (Rzeznik) who made both moms and daughters swoon, including one who apparently passed out, maybe from "one too many elephant ears," as Rzeznik joked; a crazy partner (bassist Robby Takac) w