Fix kenwood AG command to use vfo+level format instead of just level

Some rigs say 0 is the default and need to find out if 1 causes an error
If it does we need to have rig exceptions -- hopefully it's ignored
https://github.com/Hamlib/Hamlib/issues/304

rigs/kenwood/kenwood.c

@@ -724,6 +724,7 @@ int kenwood_open(RIG *rig)
             rig_debug(RIG_DEBUG_TRACE, "%s: got PS0 so powerup\n", __func__);
             rig_set_powerstat(rig, 1);
         }
+
         priv->poweron = 1;
 
         err = RIG_OK;  // reset our err back to OK for later checks
@@ -2153,8 +2154,14 @@ int kenwood_set_level(RIG *rig, vfo_t vfo, setting_t level, value_t val)
         break;
 
     case RIG_LEVEL_AF:
-        snprintf(levelbuf, sizeof(levelbuf), "AG%03d", kenwood_val);
-        break;
+    {
+        // some rigs only recognize 0 for vfo_set
+        // hopefully they are asking for VFOA or Main otherwise this might not work
+        // https://github.com/Hamlib/Hamlib/issues/304
+        int vfo_set = vfo == RIG_VFO_A || vfo == RIG_VFO_MAIN ? 0 : 1;
+        snprintf(levelbuf, sizeof(levelbuf), "AG%1d%03d", vfo_set, kenwood_val);
+    }
+    break;
 
     case RIG_LEVEL_RF:
         /* XXX check level range */

rigs/kenwood/kenwood.h

@@ -27,7 +27,7 @@
 #include <string.h>
 #include "token.h"
 
-#define BACKEND_VER "20200614"
+#define BACKEND_VER "20200615"
 
 #define EOM_KEN ';'
 #define EOM_TH '\r'