**Describe the bug**
When setting the parallel value in the system config to 0, nanomq doesn't seem to properly determine the number of parallel tasks needed to reliably deliver messages over a bridge. 

**Expected behavior**
When setting the system parallel value to 0, I would expect that we could send many messages very quickly through the broker and see that all of them are delivered over a bridge to EMQX broker.

**Actual Behavior**
I am noticing several dropped messages when setting the parallel value to 0. If I set the parallel configuration to 255 I notice only a couple of lost messages. If I set the configuration value to 1024 ([outside the documented value](https://nanomq.io/docs/en/latest/config-description/broker.html)), then I see no lost messages. We tried this value due to a suggestion found [here](https://askemq-com.translate.goog/t/topic/5872?_x_tr_sl=zh-CN&_x_tr_tl=en&_x_tr_hl=en&_x_tr_pto=sc&_x_tr_hist=true) 

**To Reproduce**
Send 100+ messages with a small interval of 10 milliseconds to nanoMQ forwarding messages to an EMQX broker

**Environment Details**
 - NanoMQ version 
 v0.21.8-8
 - Operating system and version 
 Debian 11
 - Compiler and language used
 Go Client 
 - testing scenario
 Sending 100 messages to a topic with very small intervals (10 milliseconds)

**Client SDK**
[Go Paho ](https://github.com/eclipse/paho.golang)

Parallel tasks are not being accurately determined
This is a GitHub Issue
repo:nanomq
owner:emqx
Title : Parallel tasks are not being accurately determined
Issue date:

--- start body ---
**Describe the bug**
When setting the parallel value in the system config to 0, nanomq doesn't seem to properly determine the number of parallel tasks needed to reliably deliver messages over a bridge. 

**Expected behavior**
When setting the system parallel value to 0, I would expect that we could send many messages very quickly through the broker and see that all of them are delivered over a bridge to EMQX broker.

**Actual Behavior**
I am noticing several dropped messages when setting the parallel value to 0. If I set the parallel configuration to 255 I notice only a couple of lost messages. If I set the configuration value to 1024 ([outside the documented value](https://nanomq.io/docs/en/latest/config-description/broker.html)), then I see no lost messages. We tried this value due to a suggestion found [here](https://askemq-com.translate.goog/t/topic/5872?_x_tr_sl=zh-CN&_x_tr_tl=en&_x_tr_hl=en&_x_tr_pto=sc&_x_tr_hist=true) 

**To Reproduce**
Send 100+ messages with a small interval of 10 milliseconds to nanoMQ forwarding messages to an EMQX broker

**Environment Details**
 - NanoMQ version 
 v0.21.8-8
 - Operating system and version 
 Debian 11
 - Compiler and language used
 Go Client 
 - testing scenario
 Sending 100 messages to a topic with very small intervals (10 milliseconds)

**Client SDK**
[Go Paho ](https://github.com/eclipse/paho.golang)

--- end body ---
