Fir rig.c rig_set_split_freq_mode to use VFOB/Sub as appropriate

https://github.com/Hamlib/Hamlib/issues/665

src/rig.c

@@ -4079,7 +4079,7 @@ int HAMLIB_API rig_set_split_freq_mode(RIG *rig,
 
     // in split mode we alwasy use VFOB
     // in the future we may start using RIG_VFO_TX and let the backend figure out what VFO to use
-    vfo = RIG_VFO_B; // in split mode we always use VFOB
+    vfo = vfo_fixup(rig,RIG_VFO_B); // in split mode we always use VFOB/Sub for TX
     rig_debug(RIG_DEBUG_VERBOSE,
               "%s: vfo=%s, tx_freq=%.0f, tx_mode=%s, tx_width=%d\n", __func__,
               rig_strvfo(vfo), tx_freq, rig_strrmode(tx_mode), (int)tx_width);