Read recv timestamps from socket (posix only).

This helps a lot on Android devices where the user threads can be scheduled with low priority when the app is in the background, causing spurious significantly delayed before a packet can be read from the socket. With this patch the timestamp is taken by the kernel when the packet actually arrives.

R=juberti@chromium.org
TBR=juberti@webrtc.org

BUG=webrtc:5773

Review URL: https://codereview.webrtc.org/1944683002 .

Cr-Commit-Position: refs/heads/master@{#12850}

webrtc/examples/peerconnection/client/peer_connection_client.cc

@@ -296,7 +296,7 @@ bool PeerConnectionClient::ReadIntoBuffer(rtc::AsyncSocket* socket,
                                           size_t* content_length) {
   char buffer[0xffff];
   do {
-    int bytes = socket->Recv(buffer, sizeof(buffer));
+    int bytes = socket->Recv(buffer, sizeof(buffer), nullptr);
     if (bytes <= 0)
       break;
     data->append(buffer, bytes);