Accept incoming pings before remote answer is set to reduce connection latency.
Accept incoming pings before remote answer is set to reduce connection latency.

BUG=4068
R=juberti@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/33509004

Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: c5fd66dcdfdba3ec114cc5b5c0337eba503cee40

sippet/talk,sippet/talk,sippet/talk,sippet/talk,sippet/talk