Allow get config to work with older radio firmware

Author: renzenicolai

include/lora.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <stdbool.h>
+#include <stddef.h>
 #include <stdint.h>
 #include "driver/gpio.h"
 #include "esp_err.h"
@@ -63,6 +64,8 @@ typedef struct {
     bool     use_automatic_correction;    // Enable automatic frequency correction
 } __attribute__((packed)) lora_protocol_config_params_t;
 
+#define LORA_PROTOCOL_CONFIG_PARAMS_LEGACY_SIZE offsetof(lora_protocol_config_params_t, low_data_rate_optimization)
+
 typedef struct {
     uint16_t             errors;
     lora_protocol_chip_t chip_type;

lora.c

@@ -754,7 +754,7 @@ esp_err_t lora_get_config(lora_handle_t* handle, lora_protocol_config_params_t*
         if (result != ESP_OK) {
             return result;
         }
-        if (response_length < sizeof(lora_protocol_header_t) + sizeof(lora_protocol_config_params_t)) {
+        if (response_length < sizeof(lora_protocol_header_t) + LORA_PROTOCOL_CONFIG_PARAMS_LEGACY_SIZE) {
             ESP_LOGE(TAG, "Invalid response length: %u\r\n", response_length);
             return ESP_FAIL;
         }
@@ -767,6 +767,7 @@ esp_err_t lora_get_config(lora_handle_t* handle, lora_protocol_config_params_t*
             ESP_LOGE(TAG, "Invalid response type: %u\r\n", header->type);
             return ESP_FAIL;
         }
+
         lora_protocol_config_params_t* params =
             (lora_protocol_config_params_t*)(response + sizeof(lora_protocol_header_t));
         memcpy(out_config, params, sizeof(lora_protocol_config_params_t));