Netdev revamp (#145)

* begin working on netdev solution

* need to roll back some assumptions in next commit

* dual poll/async mode for netdev.Runner

* add wake on rx semantics

* remove TODO

* more reworking of Runner

* work on applying @MDr164 suggestions and a couple extra revamps

* add newline to end of test file

examples/_import_examples/picow-netdev/main.go

@@ -70,14 +70,25 @@ func main() {
 	failIfErr("init iface", err)
 
 	go func() {
-		if err := runner.Run(context.Background(), iface, &stack, backoff); err != nil {
+		err := runner.Configure(netdev.RunnerConfig[ConnectParams]{
+			Buffers: iface.RunnerBuffers(1),
+			Backoff: backoff,
+			Flags:   netdev.RunnerInterfaceAsync | netdev.RunnerInterfacePoll,
+		})
+		if err != nil {
+			failIfErr("runnerconfig", err)
+		}
+		if err := runner.Run(context.Background(), &iface, &stack); err != nil {
 			failIfErr("runner", err)
 		}
 	}()
 	assigned, gatewayRt, subnetBits, err := stack.EnableDHCP(context.Background(), true, netip.Addr{})
 	failIfErr("enable dhcp", err)
 	println("assigned=", assigned.String(), "gateway=", gatewayRt.String(), "subnet", subnetBits)
-	select {}
+	for {
+		runner.PrintDebug()
+		time.Sleep(2 * time.Second)
+	}
 }
 
 // compile-time guarantee of interface implementation.
@@ -142,23 +153,24 @@ func (d *Netdev) SendOffsetEthFrame(offsetTxEthFrame []byte) error {
 }
 
 // SetRecvHandler implements [netdev.DevEthernet].
+//
+// The cyw43439 delivers received Ethernet frames through this callback whenever
+// the bus is serviced (including ioctl/control transactions outside EthPoll), so
+// the runner must drive it in async mode. EthPoll is still used to pump the device.
 func (d *Netdev) SetEthRecvHandler(handler func(rxEthframe []byte)) {
-	d.dev.RecvEthHandle(func(pkt []byte) error {
-		handler(pkt)
-		return nil
-	})
+	d.dev.RecvEthHandle(handler)
 }
 
 // EthPoll implements [netdev.DevEthernet].
 func (d *Netdev) EthPoll(buf []byte) (ethFrameOff, ethernetBytes int, err error) {
-	_, err = d.dev.PollOne()
-	return 0, 0, err
+	return d.dev.EthPoll(buf)
 }
 
 // MaxFrameSizeAndOffset implements [netdev.DevEthernet].
 func (d *Netdev) MaxFrameSizeAndOffset() (maxFrameSize int, frameOff int) {
-	return cyw43439.MaxFrameSize, 0
+	return 2048, 0
 }
+
 func failIfErr(msg string, err error) {
 	if err != nil {
 		fail(msg, err)