fix windows

lib/mux/sysGetsock_nowindows.go

@@ -0,0 +1,34 @@
+// +build !windows
+
+package mux
+
+import (
+	"errors"
+	"net"
+	"os"
+	"syscall"
+)
+
+func sysGetSock(fd *os.File) (bufferSize int, err error) {
+	return syscall.GetsockoptInt(int(fd.Fd()), syscall.SOL_SOCKET, syscall.SO_RCVBUF)
+}
+
+func getConnFd(c net.Conn) (fd *os.File, err error) {
+	switch c.(type) {
+	case *net.TCPConn:
+		fd, err = c.(*net.TCPConn).File()
+		if err != nil {
+			return
+		}
+		return
+	case *net.UDPConn:
+		fd, err = c.(*net.UDPConn).File()
+		if err != nil {
+			return
+		}
+		return
+	default:
+		err = errors.New("mux:unknown conn type, only tcp or kcp")
+		return
+	}
+}