Fix double tone-generator start in tone-test mode

connect() starts the tone generator but didn't set b.Tx=true,
so setTransmit would start a second instance. Now b.Tx is set
so the UI toggle works as a stop/restart instead of double-start.

client.go

@@ -59,6 +59,7 @@ func (b *Barnard) connect(reconnect bool) bool {
 		// Start the tone generator goroutine.
 		b.toneTestStop = make(chan struct{})
 		go StartToneGenerator(b.Client, b.toneTestStop)
+		b.Tx = true
 
 		// Attach the audio file saver.
 		saver, err := NewAudioFileSaver(b.ToneTestOutput)