Limits the send and receive buffer by bytes, not by packets.
The new limit is 16MB for each buffer.
Also refactors the code to handle send failure more consistently.

BUG=3429
R=juberti@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/21559005

git-svn-id: http://webrtc.googlecode.com/svn/trunk@6511 4adac7df-926f-26a2-2b94-8c16560cd09d