Add A_B_ONLY when VFO_TX is requested in vfo_fixup

https://github.com/Hamlib/Hamlib/issues/957

src/misc.c

@@ -1945,6 +1945,8 @@ vfo_t HAMLIB_API vfo_fixup(RIG *rig, vfo_t vfo, split_t split)
 
         else if (VFO_HAS_MAIN_SUB_A_B_ONLY && satmode) { vfo = RIG_VFO_SUB; }
 
+        else if (VFO_HAS_A_B_ONLY) { vfo = split ? RIG_VFO_B : RIG_VFO_A; }
+
         rig_debug(RIG_DEBUG_TRACE,
                   "%s: RIG_VFO_TX changed to %s, split=%d, satmode=%d\n", __func__,
                   rig_strvfo(vfo), split, satmode);