Update echo server tool link in IPv6 demo (FreeRTOS#1063)

Author: ActoryOu

FreeRTOS-Plus/Demo/FreeRTOS_Plus_TCP_IPv6_Demo/IPv6_Multi_WinSim_demo/ReadMe.md

@@ -189,4 +189,4 @@ The UDP Echo Client demo also demonstrates the UDP zero copy for both IPv4 and I
 UDPEchoClient_SingleTasks.c file to 1.
 
 #### Sample TCP server in Go:
-[TCP Echo Server](https://github.com/aws/amazon-freertos/tree/main/tools/echo_server)
+[TCP Echo Server](https://github.com/FreeRTOS/FreeRTOS-Libraries-Integration-Tests/tree/main/tools/echo_server)