Nikkei falls as investors pocket quick gains on Softbank

* Nikkei heavyweight Softbank falls on profit-taking after Alibaba * Hedge funds lock in gains after massive buying late last week * Broader market firmer, Topix still near 6-year high * Banks and insurers rise * Mitsubishi Motor up after tie-up with Fiat By Hideyuki Sano TOKYO, Sept 22 (Reuters) - Japan's Nikkei share average dropped on Monday as investors booked gains in heavyweight Softbank after the listing of Alibaba Group Holding Ltd , but the broader market held f