chore(gw): improve the default confs

apps/emqx_gateway/etc/emqx_gateway.conf

@@ -129,7 +129,7 @@ gateway.coap {
 
     ## DTLS Options
     ## See #{example_common_dtls_options} for more information
-    dtls.versions = ["dtlsv1"]
+    dtls.versions = ["dtlsv1.2", "dtlsv1"]
     dtls.keyfile = "{{ platform_etc_dir }}/certs/key.pem"
     dtls.certfile = "{{ platform_etc_dir }}/certs/cert.pem"
     dtls.cacertfile = "{{ platform_etc_dir }}/certs/cacert.pem"
@@ -182,6 +182,26 @@ gateway.mqttsn {
     max_connections = 10240000
     max_conn_rate = 1000
   }
+
+  listeners.dtls.default {
+    bind = 1885
+    acceptors = 4
+    max_connections = 102400
+    max_conn_rate = 1000
+
+    ## UDP Options
+    ## See ${example_common_udp_options} for more information
+    udp.active_n = 100
+    udp.buffer = 16KB
+
+    ## DTLS Options
+    ## See #{example_common_dtls_options} for more information
+    dtls.versions = ["dtlsv1.2", "dtlsv1"]
+    dtls.keyfile = "{{ platform_etc_dir }}/certs/key.pem"
+    dtls.certfile = "{{ platform_etc_dir }}/certs/cert.pem"
+    dtls.cacertfile = "{{ platform_etc_dir }}/certs/cacert.pem"
+  }
+
 }
 
 gateway.lwm2m {

apps/emqx_gateway/src/emqx_gateway_schema.erl

@@ -96,7 +96,6 @@ fields(lwm2m_structs) ->
     , {lifetime_max, sc(duration())}
     , {qmode_time_windonw, sc(integer())}
     , {auto_observe, sc(boolean())}
-    , {mountpoint, sc(string())}
     , {update_msg_publish_condition, sc(union([always, contains_object_list]))}
     , {translators, sc(ref(translators))}
     , {listeners, sc(ref(udp_listener_group))}
@@ -270,7 +269,7 @@ gateway_common_options() ->
     [ {enable, sc(boolean(), true)}
     , {enable_stats, sc(boolean(), true)}
     , {idle_timeout, sc(duration(), <<"30s">>)}
-    , {mountpoint, sc(binary(), undefined)}
+    , {mountpoint, sc(binary(), <<>>)}
     , {clientinfo_override, sc(ref(clientinfo_override))}
     , {authentication,  sc(hoconsc:lazy(map()))}
     ].