clean up dial functions

* add a context to all Dial functions
* remove the explicit Dial{*}Context functions

integrationtests/self/packetization_test.go

@@ -45,6 +45,7 @@ var _ = Describe("Packetization", func() {
 
 		clientTracer := newPacketTracer()
 		conn, err := quic.DialAddr(
+			context.Background(),
 			fmt.Sprintf("localhost:%d", proxy.LocalPort()),
 			getTLSClientConfig(),
 			getQuicConfig(&quic.Config{