add amqp prefetch_count option
diff --git a/metadata/service/server/amqp/router.yml b/metadata/service/server/amqp/router.yml
index f929c7a..ba1f8f0 100644
--- a/metadata/service/server/amqp/router.yml
+++ b/metadata/service/server/amqp/router.yml
@@ -17,6 +17,7 @@
           exchange_type: fanout
           decoder: ProtoBufDecoder
           splitter: HekaFramingSplitter
+          prefetch_count: 20
         rsyslog_kern:
           engine: logstreamer
           log_directory: /var/log