diag(icom net): name the audio stream when CI-V goes quiet

The RX audio stream is experimental and shares the rig's session with
CI-V. The shape in an operator's log is unmistakable: audio packets
arriving by the hundred while not one CI-V reply comes back, the watchdog
tearing the session down, twenty seconds' pause, and the whole thing
again — read from outside as "the Icom keeps disconnecting", with
nothing pointing at the switch that would end it.

The log now says it, and names the setting. icomAudio counts what it has
delivered so the line distinguishes "audio is enabled" from "audio is
arriving", which is the half that makes it a suspect.

internal/cat/icomaudio.go

@@ -67,12 +67,26 @@ type icomAudio struct {
 	txOuter uint16
 	txSend  uint16
 	lastRx  atomic.Int64 // UnixNano of last packet (liveness)
+	rxCount atomic.Int64 // packets delivered on this stream
 
 	done      chan struct{}
 	closeOnce sync.Once
 }
 
-func (a *icomAudio) markRx() { a.lastRx.Store(time.Now().UnixNano()) }
+func (a *icomAudio) markRx() {
+	a.lastRx.Store(time.Now().UnixNano())
+	a.rxCount.Add(1)
+}
+
+// packets reports whether the stream is actually delivering — the difference
+// between "audio is on" and "audio is arriving", which is what makes it worth
+// naming as a suspect when CI-V has gone quiet on the same session.
+func (a *icomAudio) packets() int64 {
+	if a == nil {
+		return 0
+	}
+	return a.rxCount.Load()
+}
 
 // Close tears the audio stream down (disconnect a few times; UDP is lossy).
 func (a *icomAudio) Close() {