Update relay/channel/openai/adaptor.go

use review's suggestion

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

relay/channel/openai/adaptor.go

@@ -159,9 +159,11 @@ func (a *Adaptor) ConvertOpenAIRequest(c *gin.Context, info *relaycommon.RelayIn
 	if info.ChannelType != common.ChannelTypeOpenAI && info.ChannelType != common.ChannelTypeAzure {
 		request.StreamOptions = nil
 	}
-	if info.ChannelType == common.ChannelTypeOpenRouter {
-		request.Usage = json.RawMessage("{\"include\": true}")
-	}
+if info.ChannelType == common.ChannelTypeOpenRouter {
+    if len(request.Usage) == 0 {
+        request.Usage = json.RawMessage(`{"include":true}`)
+    }
+}
 	if strings.HasPrefix(request.Model, "o") {
 		if request.MaxCompletionTokens == 0 && request.MaxTokens != 0 {
 			request.MaxCompletionTokens = request.MaxTokens