Update TCP Qemu echo demo port number macro naming in readme (FreeRTOS#1306)

Co-authored-by: Rahul Kar <118818625+kar-rahul-aws@users.noreply.github.com>

Author: tony-josi-aws

FreeRTOS-Plus/Demo/FreeRTOS_Plus_TCP_Echo_Qemu_mps2/Readme_TapNetworking.md

@@ -316,10 +316,10 @@ echo $ECHO_SERVER_IP_ADDRESS
 
 7. The echo server is assumed to be on port 7, which is the standard echo
 protocol port. You can change the port to any other listening port (e.g. 3682 ).
-Set `configECHO_PORT` to the value of this port.
+Set `echoECHO_PORT` to the value of this port.
 
 ```c
-#define configECHO_PORT          ( 7 )
+#define echoECHO_PORT          ( 7 )
 ```
 
 8. Build:

FreeRTOS-Plus/Demo/FreeRTOS_Plus_TCP_Echo_Qemu_mps2/Readme_UserNetworking.md

@@ -92,10 +92,10 @@ Do the following steps on the host machine:
 
 1. The echo server is assumed to be on port 7, which is the standard echo
 protocol port. You can change the port to any other listening port (e.g. 3682 ).
-Set `configECHO_PORT` to the value of this port.
+Set `echoECHO_PORT` to the value of this port.
 
 ```c
-#define configECHO_PORT          ( 7 )
+#define echoECHO_PORT          ( 7 )
 ```
 
 2. Build: