fix(kenwood): split frequencies swapped on transmit

IF reports the VFO "in use". In split that is the RECEIVE VFO while receiving
and the TRANSMIT VFO while transmitting — the backend took it as the receive VFO
in both cases. Everything therefore read correctly until the PTT closed and then
reversed, which is exactly how it was reported from a TS-590 on USB.

The IF frame has carried the transmit bit all along; parseKenwoodIF already
decoded it into f.TX. It was simply never consulted here.

This is not only a display fault. FreqHz is what a QSO is LOGGED on, so a
contact worked in split went into the log on the DX's frequency instead of the
operator's — wrong in the log, wrong in every ADIF exported from it, and
invisible until someone checked a QSO by hand.

The emulated rig in the test package can now be keyed, so the case is pinned
from both sides: verified failing without the fix (tx and rx exchanged) and
passing with it.

internal/cat/kenwood.go

@@ -377,16 +377,36 @@ func (k *Kenwood) ReadState() (RigState, error) {
 	f.Split = split
 
 	if f.Split {
-		// The transmit VFO is the other one. Read it rather than assume, and fall
-		// back to simplex if it cannot be read: a wrong TX frequency is written
-		// into the log, which is worse than showing no split at all.
+		// The OTHER VFO is the one IF did not report. Read it rather than assume,
+		// and fall back to simplex if it cannot be read: a wrong TX frequency is
+		// written into the log, which is worse than showing no split at all.
 		other := "FB;"
 		if f.VFO == "B" {
 			other = "FA;"
 		}
+		var otherHz int64
 		if r, err := k.ask(other); err == nil {
 			if hz, ok := parseKenwoodFreq(r, strings.TrimSuffix(other, ";")); ok && hz > 0 && hz != rx {
-				tx = hz
+				otherHz = hz
+			}
+		}
+		if otherHz > 0 {
+			// WHICH of the two is the transmit frequency depends on whether the rig
+			// is transmitting RIGHT NOW.
+			//
+			// IF reports the VFO "in use", and in split that is the RECEIVE VFO on
+			// receive and the TRANSMIT VFO on transmit. The code took it as the
+			// receive VFO always, so the moment the operator keyed up the two
+			// frequencies swapped: correct on receive, reversed on transmit, which
+			// is exactly how it was reported from a TS-590 on USB.
+			//
+			// It matters beyond the display. FreqHz is what a QSO is logged on, and
+			// a contact made in split would have gone into the log on the DX's
+			// frequency instead of the operator's.
+			if f.TX {
+				tx, rx = rx, otherHz
+			} else {
+				tx = otherHz
 			}
 		}
 	}