Properly shut down the SCTP stack.

TBR phoglund@webrtc.org for the tsan_v2/suppressions.txt change.
R=ldixon@webrtc.org, pthatcher@webrtc.org
TBR=phoglund@webrtc.org
BUG=2749

Review URL: https://webrtc-codereview.appspot.com/12739004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@6484 4adac7df-926f-26a2-2b94-8c16560cd09d