Add PTT check in set_freq since rig cannot set freq while transmitting

VOX mode was a problem so this ptt check should fix it.
https://github.com/Hamlib/Hamlib/issues/1052

rigs/yaesu/ft857.c

@@ -248,7 +248,7 @@ const struct rig_caps ft857_caps =
     RIG_MODEL(RIG_MODEL_FT857),
     .model_name =     "FT-857",
     .mfg_name =       "Yaesu",
-    .version =        "20220407.0",
+    .version =        "20220603.0",
     .copyright =      "LGPL",
     .status =         RIG_STATUS_STABLE,
     .rig_type =       RIG_TYPE_TRANSCEIVER,
@@ -936,11 +936,24 @@ int ft857_get_dcd(RIG *rig, vfo_t vfo, dcd_t *dcd)
 int ft857_set_freq(RIG *rig, vfo_t vfo, freq_t freq)
 {
     unsigned char data[YAESU_CMD_LENGTH - 1];
+    int retval;
+    int i;
+    ptt_t ptt = RIG_PTT_ON;
 
     rig_debug(RIG_DEBUG_VERBOSE, "%s: called \n", __func__);
 
     rig_debug(RIG_DEBUG_VERBOSE, "ft857: requested freq = %"PRIfreq" Hz\n", freq);
 
+    // cannot set freq while PTT is on
+    for (i = 0; i < 10 && ptt == RIG_PTT_ON; ++i)
+    {
+        retval = rig_get_ptt(rig, vfo, &ptt);
+
+        if (retval != RIG_OK) { return retval; }
+
+        hl_usleep(100 * 1000);
+    }
+
     /* fill in the frequency */
     to_bcd_be(data, (freq + 5) / 10, 8);