After echo check to a get_freq in icom.c

Should fix poweron for Icom rigs that still echo in standby mode
https://github.com/Hamlib/Hamlib/issues/583

rigs/icom/icom.c

@@ -761,6 +761,14 @@ icom_rig_open(RIG *rig)
               rig->caps->version);
     retval = icom_get_usb_echo_off(rig);
 
+    if (retval == RIG_OK) // then echo is on so let's try freq now
+    {
+        // some rigs like the IC7100 still echo when in standby
+        // so asking for freq now should timeout if such a rig
+        freq_t tfreq;
+        retval = rig_get_freq(rig,RIG_VFO_A,&tfreq);
+    }
+
     if (retval != RIG_OK && priv->poweron == 0 && rs->auto_power_on)
     {
         // maybe we need power on?

rigs/icom/icom.h

@@ -30,7 +30,7 @@
 #include <sys/time.h>
 #endif
 
-#define BACKEND_VER "20210304"
+#define BACKEND_VER "20210305"
 
 /*
  * defines used by comp_cal_str in rig.c