add Allow0RTT opt in the quic.Config to control 0-RTT on the server side (#3635)

connection.go

@@ -241,7 +241,6 @@ var newConnection = func(
 	conf *Config,
 	tlsConf *tls.Config,
 	tokenGenerator *handshake.TokenGenerator,
-	enable0RTT bool,
 	clientAddressValidated bool,
 	tracer logging.ConnectionTracer,
 	tracingID uint64,
@@ -323,6 +322,10 @@ var newConnection = func(
 	if s.tracer != nil {
 		s.tracer.SentTransportParameters(params)
 	}
+	var allow0RTT func() bool
+	if conf.Allow0RTT != nil {
+		allow0RTT = func() bool { return conf.Allow0RTT(conn.RemoteAddr()) }
+	}
 	cs := handshake.NewCryptoSetupServer(
 		initialStream,
 		handshakeStream,
@@ -340,7 +343,7 @@ var newConnection = func(
 			},
 		},
 		tlsConf,
-		enable0RTT,
+		allow0RTT,
 		s.rttStats,
 		tracer,
 		logger,