Fix kenwood cache IF len -- have to remove terminator

https://github.com/Hamlib/Hamlib/issues/226

rigs/kenwood/kenwood.c

@@ -532,7 +532,7 @@ transaction_quit:
     if (strcmp(cmdstr, "IF") == 0)
     {
         elapsed_ms(&priv->cache_start, 1);
-        strncpy(priv->last_if_response, buffer, sizeof(priv->last_if_response));
+        strncpy(priv->last_if_response, buffer, caps->if_len);
     }
 
     rs->hold_decode = 0;

rigs/kenwood/kenwood.h

@@ -27,7 +27,7 @@
 #include <string.h>
 #include "token.h"
 
-#define BACKEND_VER "20200428"
+#define BACKEND_VER "20200429"
 
 #define EOM_KEN ';'
 #define EOM_TH '\r'