[Master] Goroutine leaks when consumer restart frequently

[maixiaohai]

BUG REPORT

1. Please describe the issue you observed:

   • What did you do (The steps to reproduce)?
     We have a logic to manage different pushConsumer as task. So we need to restart pushConsumer with same subscription in the same process.
   • What did you expect to see?
     start consumer with no new message come, the sleep 3 second, shutdown the consumer.The goroutine number not increase with the start and shutdown.
   • What did you see instead?
     The number of goroutine increase.

2. Please tell us about your environment:

   • What is your OS?
     Centos 7
   • What is your client version?
     v2.1.0-rc5
   • What is your RocketMQ version?
     v4.7.0 / v4.8.0

3. Other information (e.g. detailed explanation, logs, related issues, suggestions on how to fix, etc):
   msgCh should be closed when consumer shutdown?

[maixiaohai]

After fix