Fix bug in TCP implementation (simulations).

The problem was that only ACKed packets were subtracted from in_flight_, but lost packets were never removed, which caused TCP to stop sending eventually.

R=pbos@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/43239004

Cr-Commit-Position: refs/heads/master@{#9041}
2 files changed