Provide better message for when RTCP mux "require" policy is triggered.

Provide better message for when RTCP mux "require" policy is triggered.

Previously: Failed to setup RTCP mux filter.
Now: rtcpMuxPolicy is 'require', but media description does not
     contain 'a=rtcp-mux'.

BUG=webrtc:6966
Review-Url: https://codereview.webrtc.org/2622553003
Cr-Commit-Position: refs/heads/master@{#16062}
Committed: https://chromium.googlesource.com/external/webrtc/+/8e814d79063c30435ef3bfa0da40661ba0846c94

[pthatcher1, 2017-01-11 21:30:19]

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

[pthatcher1, 2017-01-11 21:30:20]

lgtm

[Taylor Brandstetter, 2017-01-13 18:34:26]

The CQ bit was checked by deadbeef@webrtc.org

[commit-bot: I haz the power, 2017-01-13 18:34:29]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.webrtc.org/...

[commit-bot: I haz the power, 2017-01-13 19:34:40]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1484332466591410, "parent_rev":
"482c539ac7e3d4fdfd1f3bb06be709ae0c8d0be7", "commit_rev":
"8e814d79063c30435ef3bfa0da40661ba0846c94"}

[commit-bot: I haz the power, 2017-01-13 19:34:42]

Description was changed from

==========
Provide better message for when RTCP mux "require" policy is triggered.

Previously: Failed to setup RTCP mux filter.
Now: rtcpMuxPolicy is 'require', but media description does not
     contain 'a=rtcp-mux'.

BUG=webrtc:6966
==========

to

==========
Provide better message for when RTCP mux "require" policy is triggered.

Previously: Failed to setup RTCP mux filter.
Now: rtcpMuxPolicy is 'require', but media description does not
     contain 'a=rtcp-mux'.

BUG=webrtc:6966

Review-Url: https://codereview.webrtc.org/2622553003
Cr-Commit-Position: refs/heads/master@{#16062}
Committed:
https://chromium.googlesource.com/external/webrtc/+/8e814d79063c30435ef3bfa0d...
==========

[commit-bot: I haz the power, 2017-01-13 19:34:43]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/external/webrtc/+/8e814d79063c30435ef3bfa0d...