Increase STUN RTOs to work better on poor networks, such as 2G networks.

BUG=b/34822484

Review-Url: https://codereview.webrtc.org/2677743002
Cr-Original-Commit-Position: refs/heads/master@{#16503}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 94a2f21c0573be1d909c9df157deb08bd9650262
7 files changed