Fix configure file parse

cmd/chihaya/config.go

@@ -23,7 +23,7 @@ type hookConfig struct {
 // ConfigFile represents a namespaced YAML configation file.
 type ConfigFile struct {
 	MainConfigBlock struct {
-		middleware.Config
+		middleware.Config `yaml:",inline"`
 		PrometheusAddr    string              `yaml:"prometheus_addr"`
 		HTTPConfig        httpfrontend.Config `yaml:"http"`
 		UDPConfig         udpfrontend.Config  `yaml:"udp"`