Nikkei's gains limited by worries over Japan's recovery

* Nikkei up slightly, led by gains in constructors * Fears of bigger-than-expected sales tax hike impact cap gains * Nisshin Steel sinks on share offering By Hideyuki Sano TOKYO, Sept 1 (Reuters) - Japanese shares edged up on Monday, led by gains in some mid- and small-cap shares, but the advance was mostly capped on worries the Japanese economic recovery from a tax hike earlier this year may be weaker than initially thought. The Nikkei share average rose 0.2 percent to 15,4