fix(congestion): fix congestion message formatting

It seems that the `~ts` in the format string does not handle maps,
which results in a crash when trying to format the congestion message.

```erlang
28> io_lib:format("~ts", [#{}]).
** exception error: bad argument
     in function  io_lib:format/2
        called as io_lib:format("~ts",[#{}])
```

Example:

```
2022-03-04T12:43:26.900609+00:00 [warning] '$kind': unclean_terminate, clientid: 192.168.2.116_bench_sub_11412_1782328074, context: badarg, exception: error, line: 582, mfa: emqx_connection:terminate/2, peername: 192.168.2.116:47358, stacktrace: [{io_lib,format,["connection congested: ~ts",[#{buffer => 4096,clientid => <<"192.168.2.116_bench_sub_11412_1782328074">>,conn_state => disconnected,connected_at => 1646397524470,high_msgq_watermark => 8192,high_watermark => 1048576,memory => 57064,message_queue_len => 20,peername => <<"192.168.2.116:47358">>,pid => <<"<0.259.28>">>,proto_name => <<"MQTT">>,proto_ver => 5,recbuf => 4096,recv_cnt => 2,recv_oct => 81,reductions => 267523,send_cnt => 333,send_oct => 149869,send_pend => 128,sndbuf => 332800,sockname => <<"10.10.1.13:1883">>,socktype => tcp,username => undefined}]],[{file,"io_lib.erl"},{line,187}]},{emqx_congestion,do_cancel_alarm_congestion,4,[{file,"/emqx/apps/emqx/src/emqx_congestion.erl"},{line,88}]},{lists,foreach,2,[{file,"lists.erl"},{line,1342}]},{emqx_connection,terminate,2,[{file,"/emqx/apps/emqx/src/emqx_connection.erl"},{line,576}]},{proc_lib,wake_up,3,[{file,"proc_lib.erl"},{line,236}]}]
```

apps/emqx/src/emqx_congestion.erl

@@ -78,14 +78,14 @@ cancel_alarm_congestion(Socket, Transport, Channel, Reason) ->
 do_alarm_congestion(Socket, Transport, Channel, Reason) ->
     ok = update_alarm_sent_at(Reason),
     AlarmDetails = tcp_congestion_alarm_details(Socket, Transport, Channel),
-    Message = io_lib:format("connection congested: ~ts", [AlarmDetails]),
+    Message = io_lib:format("connection congested: ~p", [AlarmDetails]),
     emqx_alarm:activate(?ALARM_CONN_CONGEST(Channel, Reason), AlarmDetails, Message),
     ok.
 
 do_cancel_alarm_congestion(Socket, Transport, Channel, Reason) ->
     ok = remove_alarm_sent_at(Reason),
     AlarmDetails = tcp_congestion_alarm_details(Socket, Transport, Channel),
-    Message = io_lib:format("connection congested: ~ts", [AlarmDetails]),
+    Message = io_lib:format("connection congested: ~p", [AlarmDetails]),
     emqx_alarm:deactivate(?ALARM_CONN_CONGEST(Channel, Reason), AlarmDetails, Message),
     ok.
 

apps/emqx/test/emqx_connection_SUITE.erl

@@ -432,6 +432,32 @@ t_oom_shutdown(_) ->
       end, Opts),
     ok.
 
+t_cancel_congestion_alarm(_) ->
+    Opts = #{trap_exit => false},
+    ok = meck:expect(emqx_transport, getstat,
+                     fun(_Sock, [send_pend]) ->
+                             %% simulate congestion
+                             {ok, [{send_pend, 999}]};
+                        (_Sock, Options) ->
+                             {ok, [{K, 0} || K <- Options]}
+                     end),
+    with_conn(
+      fun(Pid) ->
+              #{ channel := Channel
+               , transport := Transport
+               , socket := Socket
+               } = emqx_connection:get_state(Pid),
+              %% precondition
+              Zone = emqx_channel:info(zone, Channel),
+              true = emqx_config:get_zone_conf(Zone, [conn_congestion, enable_alarm]),
+              %% should not raise errors
+              ok = emqx_congestion:maybe_alarm_conn_congestion(Socket, Transport, Channel),
+              %% should not raise errors either
+              ok = emqx_congestion:cancel_alarms(Socket, Transport, Channel),
+              ok
+      end, Opts),
+    ok.
+
 %%--------------------------------------------------------------------
 %% Helper functions
 %%--------------------------------------------------------------------