feat: update MaxTokens handling

relay/channel/perplexity/relay-perplexity.go

@@ -16,6 +16,6 @@ func requestOpenAI2Perplexity(request dto.GeneralOpenAIRequest) *dto.GeneralOpen
 		Messages:    messages,
 		Temperature: request.Temperature,
 		TopP:        request.TopP,
-		MaxTokens:   request.MaxTokens,
+		MaxTokens:   request.GetMaxTokens(),
 	}
 }