Allows detecting large-enough audio packets as part of a probe, speculative fix for a rampup-time regression in M50. These packets are accounted on the send side when probing. BUG=webrtc:5985 R=mflodman@webrtc.org, philipel@webrtc.org Review URL: https://codereview.webrtc.org/2061193002 . Cr-Commit-Position: refs/heads/master@{#13210}