Allow p2p UDP packages to set DSCP

net/udp/udp_socket_libevent.cc

Index: net/udp/udp_socket_libevent.cc
diff --git a/net/udp/udp_socket_libevent.cc b/net/udp/udp_socket_libevent.cc
index 90c7da6504103dead9150b5cf28adde33b598f5f..dd1ec598d5dfb66f8bbf755899b8e954fa2f89e9 100644
--- a/net/udp/udp_socket_libevent.cc
+++ b/net/udp/udp_socket_libevent.cc
@@ -651,4 +651,24 @@ int UDPSocketLibevent::SetMulticastLoopbackMode(bool loopback) {
     socket_options_ &= ~SOCKET_OPTION_MULTICAST_LOOP;
   return OK;
 }
+
+int UDPSocketLibevent::SetToS(DiffServCodePoint dscp) {
+  if (dscp == DSCP_NO_CHANGE) {
+    return OK;
+  }
+  int rv;
+  int dscp_and_ecn = dscp << 2;
+  if (addr_family_ == AF_INET) {
+    rv = setsockopt(socket_, IPPROTO_IP, IP_TOS,
+                    &dscp_and_ecn, sizeof(dscp_and_ecn));
+  } else {
+    rv = setsockopt(socket_, IPPROTO_IPV6, IPV6_TCLASS,
+                    &dscp_and_ecn, sizeof(dscp_and_ecn));
+  }
+  if (rv < 0)
+    return MapSystemError(errno);
+
+  return OK;
+}
+
 }  // namespace net