Fix memory_breakdown for connection procs

Instead of trying to read the ranch_server ETS table directly,
use an internal Ranch function that does the same. While neither
are documented, the latter is less likely to change.

Author: Loïc Hoguin

deps/rabbit/src/rabbit_vm.erl

@@ -231,7 +231,7 @@ conn_sups()     ->
 
 ranch_server_sups() ->
     try
-        ets:match(ranch_server, {{conns_sup, '_'}, '$1'})
+        [Pid || {_, _, Pid} <- ranch_server:get_connections_sups()]
     catch
         %% Ranch ETS table doesn't exist yet
         error:badarg  -> []

release-notes/3.9.8.md

@@ -25,6 +25,10 @@ Contributors are encouraged to update them together with their changes. This hel
 
    GitHub issue: [#3445](https://github.com/rabbitmq/rabbitmq-server/issues/3560)
 
+* `rabbitmq-diagnostics memory_breakdown` failed to read memory of connection
+  reader, writer and channel processes.
+
+   GitHub issue: [#3445](https://github.com/rabbitmq/rabbitmq-server/issues/3560)
 
 ## Dependency Upgrades