floss: metrics: Fix pkt loss metrics

Zero lost frames should be legal.
Lower log level for the noisy corrupted mSBC packet log.

BUG: 239978865
Tag: #floss
Test: ./build.py
Test: emerge-${BOARD} floss
Test: gd/cert/run
Change-Id: I4dc5f565e88c5157c92a8023951f4993690f61ff