bug fix:并发读写map问题;add:新增Stop()函数

libpcap/libpcap.go

@@ -60,6 +60,7 @@ func NewCatchEth(eth string, sentence string) (*NetCatch, error) {
 	nc := new(NetCatch)
 	nc.eth = eth
 	nc.sentence = sentence
+	nc.ctx, nc.stopFn = context.WithCancel(context.Background())
 	return nc, nil
 }