chore(gw): reformat config options

apps/emqx_gateway/etc/emqx_gateway.conf

@@ -2,10 +2,10 @@
 ## EMQ X Gateway configurations
 ##--------------------------------------------------------------------
 
-gateway: {
-
-  stomp: {
+## TODO: These configuration options are temporary example here.
+## In the final version, it will be commented out.
 
+gateway.stomp {
   frame: {
     max_headers: 10
     max_headers_length: 1024
@@ -38,10 +38,11 @@ gateway: {
   }
 }
 
-  coap: {
+gateway.coap: {
 
   enable_stats: false
 
+  #authentication.enable: false
   authentication: {
     enable: true
     authenticators: [
@@ -54,8 +55,6 @@ gateway: {
     ]
   }
 
-    #authentication.enable: false
-
   heartbeat: 30s
   notify_type: qos
   subscribe_qos: qos0
@@ -65,7 +64,7 @@ gateway: {
   }
 }
 
-    mqttsn: {
+gateway.mqttsn: {
   ## The MQTT-SN Gateway ID in ADVERTISE message.
   gateway_id: 1
 
@@ -108,8 +107,7 @@ gateway: {
   }
 }
 
-    ## Extension Protocol Gateway
-  exproto: {
+gateway.exproto: {
   ## The gRPC server to accept requests
   server: {
     bind: 9100
@@ -139,17 +137,13 @@ gateway: {
   #listener.dtls.1: {}
 }
 
-
-  lwm2m: {
+gateway.lwm2m: {
 
   xml_dir: "{{ platform_etc_dir }}/lwm2m_xml"
 
   lifetime_min: 1s
-
   lifetime_max: 86400s
-
   qmode_time_windonw: 22
-
   auto_observe: false
 
   mountpoint: "lwm2m/%e/"
@@ -169,4 +163,3 @@ gateway: {
       bind: 5783
   }
 }
-}