Transport sequence number should be set also for retransmissions.

Transport sequence number should be set also for retransmissions.

When fetching a packet from the rtp packet history, cuased by a
retransmission, the transport seq extension header is enabled but the
sequence number is set to 0. A new transport seq should be assigned in
this case.

BUG=

Committed: https://crrev.com/af4ced986bc62c263fbdb6eab68aef5c0d4e7c78
Cr-Commit-Position: refs/heads/master@{#10183}

[sprang_webrtc, 2015-10-06 09:46:00]

sprang@webrtc.org changed reviewers:
+ stefan@webrtc.org

[stefan-webrtc, 2015-10-06 10:54:55]

lgtm

[sprang_webrtc, 2015-10-06 10:58:55]

The CQ bit was checked by sprang@webrtc.org

[commit-bot: I haz the power, 2015-10-06 10:59:08]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1385563005/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1385563005/1

[commit-bot: I haz the power, 2015-10-06 13:02:58]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-06 13:03:08]

Patchset 1 (id:??) landed as
https://crrev.com/af4ced986bc62c263fbdb6eab68aef5c0d4e7c78
Cr-Commit-Position: refs/heads/master@{#10183}