BrokerName is null when using pop model to consume msgs

[cserwen]

BUG REPORT

1. Please describe the issue you observed:

• What did you do (The steps to reproduce)?
  Using pop model to consume msg or using console to resend msg directly.

• What is expected to see?
  The brokerName of msg should not be null.

• What did you see instead?
  It is null

2. Please tell us about your environment:
   5.0.0-beta.

3. Other information (e.g. detailed explanation, logs, related issues, suggestions on how to fix, etc):
   Set it when client reveives msgs.