move ECONNRESET log from error to debug (#1363)

* move ECONNRESET log from error to debug

* move client errors to debug

fastify.js

@@ -786,7 +786,7 @@ function build (options) {
       message: 'Client Error',
       statusCode: 400
     })
-    log.error({ err }, 'client error')
+    log.debug({ err }, 'client error')
     socket.end(`HTTP/1.1 400 Bad Request\r\nContent-Length: ${body.length}\r\nContent-Type: application/json\r\n\r\n${body}`)
   }