CompactNtpIntervalToMs renamed to CompactNtpRttToMs and handle special cases: large values consider negative/invalid and result in value of 1. 0 result consider too small and increases to 1. BUG=590996 R=asapersson@webrtc.org, stefan@webrtc.org Review URL: https://codereview.webrtc.org/1763823003 . Cr-Commit-Position: refs/heads/master@{#11928}