Fix Turn TCP port issue.

Sometimes the port still try to send stun packet when the connection is disconnected,
causing an assertion error.

BUG=4859

Review URL: https://codereview.webrtc.org/1247573002

Cr-Original-Commit-Position: refs/heads/master@{#9671}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: b19eba3d4bbc70ece91d524e21e2e9d4253ff7a9
4 files changed