Fix maxMessageSize not effective even if aligned with broker

[wuYin]

Motivation

• issue 1
  If broker updated maxMessageSize, client's maxMessageSize will be the same after handshaking.
  However, client still use the default maxMessageSize while reading command from connection.
  Lead to consumer can't receive message which payload exceed 5MB.

• issue 2
  According to PIP-36, default *Size should be:

  maxMessageSize = 5MB
  framePaddingSize = 10KB
  maxFrameSize = maxMessageSize + framePaddingSize
  

  But they two are confused currently：

  maxFrameSize = 5MB
  framePaddingSize = 10KB
  maxMessageSize = maxFrameSize - framePaddingSize
  

Modifications

• Use the aligned maxMessageSize instead of the default value.
• Correct maxMessageSize default value.

Verifying this change

• Make sure that the change passes the CI checks.