esp-modem(Docs): Update documentation and minor fixes

components/esp_modem/include/esp_modem_config.h

@@ -17,6 +17,10 @@
 #include "driver/uart.h"
 #include "esp_modem_dce_config.h"
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /**
  * @defgroup ESP_MODEM_CONFIG
  * @brief Configuration structures for DTE and DCE
@@ -56,6 +60,9 @@ struct esp_modem_uart_term_config {
     int event_queue_size;           /*!< UART Event Queue Size, set to 0 if no event queue needed */
 };
 
+// Forward declare the resource struct
+struct esp_modem_vfs_resource;
+
 /**
  * @brief VFS configuration structure
  *
@@ -116,4 +123,8 @@ typedef struct esp_modem_dte_config esp_modem_dte_config_t;
  * @}
  */
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif // _ESP_MODEM_CONFIG_H_