tikv: reduce call of TiKVSendReqHistogram.WithLabelValues (#15297)
tikv: reduce call of TiKVSendReqHistogram.WithLabelValues (#15297)


ngaut/tidb,pingcap/tidb,ngaut/tidb,kyle-wang/tidb,kyle-wang/tidb,pingcap/tidb,c4pt0r/tidb,ngaut/tidb,pingcap/tidb,EvilMcJerkface/tidb,coocood/tidb,pingcap/tidb,kyle-wang/tidb,c4pt0r/tidb,c4pt0r/tidb,kyle-wang/tidb,ngaut/tidb,c4pt0r/tidb,c4pt0r/tidb,XuHuaiyu/tidb,c4pt0r/tidb,pingcap/tidb,kyle-wang/tidb,pingcap/tidb,kyle-wang/tidb,coocood/tidb,EvilMcJerkface/tidb,ngaut/tidb,ngaut/tidb,XuHuaiyu/tidb