Add filternum option for Icom rigs so WJST-X can use hamlib_settings.json to set default filter

https://github.com/Hamlib/Hamlib/issues/1507

rigs/icom/icom.c

@@ -437,6 +437,7 @@ struct icom_addr
 #define TOK_MODE731 TOKEN_BACKEND(2)
 #define TOK_NOXCHG TOKEN_BACKEND(3)
 #define TOK_TONE_ENABLE TOKEN_BACKEND(4)
+#define TOK_FILTERNUM TOKEN_BACKEND(5)
 
 const struct confparams icom_cfg_params[] =
 {
@@ -459,6 +460,10 @@ const struct confparams icom_cfg_params[] =
         "Overcome a bug in IC-705 to enable tone after frequency change",
         "0", RIG_CONF_CHECKBUTTON
     },
+    {
+        TOK_FILTERNUM, "filternum", "Filter to use", "Filter to use when setting mode",
+        "0", RIG_CONF_NUMERIC, {.n = {0, 3, 1}}
+    },
     {RIG_CONF_END, NULL,}
 };
 
@@ -2274,6 +2279,7 @@ static int icom_set_mode_x26(RIG *rig, vfo_t vfo, rmode_t mode, int datamode,
     // Skip filter selection, because at least IC-7300 has a bug defaulting to filter 2 when changing mode
     // Tested on IC-7300 and IC-9700
     buf[2] = priv->filter;
+    if (priv->filternum > 0) buf[2] = priv->filternum; // override with requested filternum
     // buf[2] = 1;
 
     int vfo_number = icom_get_vfo_number_x25x26(rig, vfo);
@@ -5014,6 +5020,12 @@ int icom_set_conf(RIG *rig, hamlib_token_t token, const char *val)
         priv->tone_enable = atoi(val) ? 1 : 0;
         break;
 
+    case TOK_FILTERNUM:
+        priv->filternum = atoi(val);
+        if (priv->filternum > 3) priv->filternum = 3;
+        if (priv->filternum < 1) priv->filternum = 1;
+        break;
+
     default:
         RETURNFUNC(-RIG_EINVAL);
     }

rigs/icom/icom.h

@@ -293,6 +293,7 @@ struct icom_priv_data
     int vfo_flag; // used to skip vfo check when frequencies are equal
     int dual_watch_main_sub; // 0=main, 1=sub
     int tone_enable;         /*!< Re-enable tone after freq change -- IC-705 bug with gpredict */
+    int filternum;           /*!< Filter number to use when setting mode */
 };
 
 extern const struct ts_sc_list r8500_ts_sc_list[];