Remove default receive channel from WVoE; baby step 2.

Remove default receive channel from WVoE; baby step 2.
Rename voe_channel_ to default_send_channel_id_.

BUG=webrtc:4690
Committed: https://crrev.com/8fb30c328b7b5e1ad33e970d1dabca55fdc18926
Cr-Commit-Position: refs/heads/master@{#10261}

[the sun, 2015-10-05 15:12:16]

solenberg@webrtc.org changed reviewers:
+ pthatcher@webrtc.org

[the sun, 2015-10-05 15:12:16]

I want to keep the renaming separate from actual removal of the default receive
channel. Intention is to submit this in sequence with
https://codereview.webrtc.org/1385893002/, once both are ready.

[pthatcher1, 2015-10-06 18:21:27]

lgtm

[the sun, 2015-10-13 10:02:17]

The CQ bit was checked by solenberg@webrtc.org

[the sun, 2015-10-13 10:02:18]

The patchset sent to the CQ was uploaded after l-g-t-m from pthatcher@webrtc.org
Link to the patchset: https://codereview.webrtc.org/1388733002/#ps100001 (title:
"rebase")

[commit-bot: I haz the power, 2015-10-13 10:02:29]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1388733002/100001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1388733002/100001

[commit-bot: I haz the power, 2015-10-13 10:07:06]

Committed patchset #6 (id:100001)

[commit-bot: I haz the power, 2015-10-13 10:07:18]

Patchset 6 (id:??) landed as
https://crrev.com/8fb30c328b7b5e1ad33e970d1dabca55fdc18926
Cr-Commit-Position: refs/heads/master@{#10261}