fix udp original destination on windows

proxy/dokodemo/fakeudp_windows.go

@@ -0,0 +1,27 @@
+//go:build windows
+// +build windows
+
+package dokodemo
+
+import (
+	"net"
+	"syscall"
+)
+
+func FakeUDP(addr *net.UDPAddr, mark int) (net.PacketConn, error) {
+	udpConn, err := net.ListenUDP("udp", addr)
+	if err != nil {
+		return udpConn, err
+	}
+	rawConn, err := udpConn.SyscallConn()
+	if err != nil {
+		return nil, err
+	}
+	err = rawConn.Control(func(fd uintptr) {
+		syscall.SetsockoptInt(syscall.Handle(fd), syscall.SOL_SOCKET, syscall.SO_REUSEADDR, 1)
+	})
+	if err != nil {
+		return nil, err
+	}
+	return udpConn, nil
+}