Enabling IPv6 socket recv timestamp test, and making less flaky.

webrtc/base/socket.h

Index: webrtc/base/socket.h
diff --git a/webrtc/base/socket.h b/webrtc/base/socket.h
index 7db9459de7ca84b4b8dff3db847b450816f563fd..73dfdbb808b5743947f096aaec6317685c71daff 100644
--- a/webrtc/base/socket.h
+++ b/webrtc/base/socket.h
@@ -151,6 +151,7 @@ class Socket {
   virtual int Connect(const SocketAddress& addr) = 0;
   virtual int Send(const void *pv, size_t cb) = 0;
   virtual int SendTo(const void *pv, size_t cb, const SocketAddress& addr) = 0;
+  // |timestamp| is in units of microseconds.
   virtual int Recv(void* pv, size_t cb, int64_t* timestamp) = 0;
   virtual int RecvFrom(void* pv,
                        size_t cb,