chore(conf): change default number of gen_rpc connections to 1

etc/emqx.conf

@@ -343,8 +343,8 @@ rpc.port_discovery = stateless
 ## Number of outgoing RPC connections.
 ##
 ## Value: Interger [0-256]
-## Defaults to NumberOfCPUSchedulers / 2 when set to 0
-#rpc.tcp_client_num = 0
+## Default = 1
+#rpc.tcp_client_num = 1
 
 ## RCP Client connect timeout.
 ##

priv/emqx.schema

@@ -376,7 +376,7 @@ end}.
 
 {translation, "gen_rpc.tcp_client_num", fun(Conf) ->
   case cuttlefish:conf_get("rpc.tcp_client_num", Conf) of
-    0 -> max(1, erlang:system_info(schedulers) div 2);
+    0 -> 1; %% keep allowing 0 for backward compatibility
     V -> V
   end
 end}.