add go-tun2socks code

core/udp_callback.go

@@ -0,0 +1,21 @@
+package core
+
+/*
+#cgo CFLAGS: -I./c/include
+#include "lwip/udp.h"
+
+extern void udpRecvFn(void *arg, struct udp_pcb *pcb, struct pbuf *p, const ip_addr_t *addr, u16_t port, const ip_addr_t *dest_addr, u16_t dest_port);
+
+void
+set_udp_recv_callback(struct udp_pcb *pcb, void *recv_arg) {
+	udp_recv(pcb, udpRecvFn, recv_arg);
+}
+*/
+import "C"
+import (
+	"unsafe"
+)
+
+func setUDPRecvCallback(pcb *C.struct_udp_pcb, recvArg unsafe.Pointer) {
+	C.set_udp_recv_callback(pcb, recvArg)
+}