Update the max length of a name in a sendValue packet (#1965)

docs/reference/radio/send-value.md

@@ -1,7 +1,7 @@
 # send Value
 
 Send a [string]() and [number]() together by ``radio`` to other @boardname@s.
-The maximum [string]() length is 12 characters.
+The maximum [string]() length is 8 characters.
 
 ```sig
 radio.sendValue("name", 0);

libs/radio/radio.cpp

@@ -259,8 +259,9 @@ namespace radio {
 
     /**
     * Broadcasts a name / value pair along with the device serial number
-    * and running time to any connected micro:bit in the group.
-    * @param name the field name (max 12 characters), eg: "name"
+    * and running time to any connected micro:bit in the group. The name can
+    * include no more than 8 characters.
+    * @param name the field name (max 8 characters), eg: "name"
     * @param value the numeric value
     */
     //% help=radio/send-value

sim/state/radio.ts

@@ -160,7 +160,7 @@ namespace pxsim.radio {
     }
 
     export function sendValue(name: string, value: number) {
-        name = name.substr(0, 12);
+        name = name.substr(0, 8);
         const msg: number[] = [];
         msg.push()
         board().radioState.datagram.send({