[mac] only append header termination IE2 when data payload is present (#6223)

According to IEEE802.15.4, header termination IE2 is present only when
header IE and payload data is present.

src/core/thread/mesh_forwarder.cpp

@@ -1553,8 +1553,8 @@ void MeshForwarder::AppendHeaderIe(const Message *aMessage, Mac::Frame &aFrame)
 {
     uint8_t index     = 0;
     bool    iePresent = false;
-
-    OT_UNUSED_VARIABLE(aMessage);
+    bool    payloadPresent =
+        (aFrame.GetType() == Mac::Frame::kFcfFrameMacCmd) || (aMessage != nullptr && aMessage->GetLength() != 0);
 
 #if OPENTHREAD_CONFIG_TIME_SYNC_ENABLE
     if (aMessage != nullptr && aMessage->IsTimeSync())
@@ -1571,8 +1571,9 @@ void MeshForwarder::AppendHeaderIe(const Message *aMessage, Mac::Frame &aFrame)
     }
 #endif
 
-    if (iePresent)
+    if (iePresent && payloadPresent)
     {
+        // Assume no Payload IE in current implementation
         IgnoreError(aFrame.AppendHeaderIeAt<Mac::Termination2Ie>(index));
     }
 }