Fix packet cbs/ebs conversion.

Each packet is counted as 128 bytes by the code, not 125. Not sure
what I was thinking about here 14 years ago. May be just a typo.

Reported by: Dmitry Luhtionov <dmitryluhtionov@gmail.com>
MFC after: 2 weeks

(cherry picked from commit 4a6830761c6552bfe2c118a73a5a461694cb84c7)