Cast: Cap max receiver log size per rtcp packet to 200 bytes.

This is a short term fix to hopefully reduce the effects of packets
queueing up on the receiver side. Previously we try fill up the RTCP
packet with as many receiver log as possible so we can have redundancy.
The redundancy that has been observed was more than 30 per message, and
we don't need this much redundancy. 200 is a good number where each
log message will be sent with redundancy of around 2-3, without losing
too many (< 1%) messages, assuming default rtcp interval settings.
That's fine because we don't need the logs to be completely reliable.


BUG=349265

Review URL: https://codereview.chromium.org/189423002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255602 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255602