fix(mgmt): node memory usage info

apps/emqx_management/src/emqx_mgmt.erl

@@ -139,7 +139,7 @@ node_info(Node) when Node =:= node() ->
     Info#{node              => node(),
           otp_release       => iolist_to_binary(otp_rel()),
           memory_total      => proplists:get_value(allocated, Memory),
-          memory_used       => proplists:get_value(total, Memory),
+          memory_used       => proplists:get_value(used, Memory),
           process_available => erlang:system_info(process_limit),
           process_used      => erlang:system_info(process_count),
           max_fds           => proplists:get_value(max_fds, lists:usort(lists:flatten(erlang:system_info(check_io)))),
@@ -570,5 +570,3 @@ max_row_limit() ->
     application:get_env(?APP, max_row_limit, ?MAX_ROW_LIMIT).
 
 table_size(Tab) -> ets:info(Tab, size).
-
-