Change initial DTLS retransmission timer from 1 second to 50ms.

This will help ensure a timely DTLS handshake when there's packet
loss. It will likely result in spurious retransmissions (since the
RTT is usually > 50ms), but since exponential backoff is still used,
there will at most be ~4 extra retransmissions. For a time-sensitive
application like WebRTC this seems like a reasonable tradeoff.

R=pthatcher@webrtc.org, juberti@chromium.org, juberti@webrtc.org

Review URL: https://codereview.webrtc.org/1981463002 .

Committed: https://crrev.com/1e435628366fb9fed71632369f05928ed857d8ef
Cr-Original-Commit-Position: refs/heads/master@{#13159}
Cr-Original-Original-Commit-Position: refs/heads/master@{#12853}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 4f0dfbd213aaad0b8b32b0cf0101b47aea039770
9 files changed