hid_device: add c++ and header guards and API flags

src/classic/hid_device.h

@@ -35,10 +35,17 @@
  *
  */
 
+#ifndef hid_device_h
+#define hid_device_h
+
 #include <stdint.h>
 #include "btstack_defines.h"
 #include "bluetooth.h"
 
+#if defined __cplusplus
+extern "C" {
+#endif
+
 /**
  * @brief Create HID Device SDP service record. 
  * @param service Empty buffer in which a new service record will be stored.
@@ -66,6 +73,8 @@ void hid_create_sdp_record(
     uint16_t 		hid_descriptor_size,
     const char *    device_name);
 
+/* API_START */
+
 /**
  * @brief Set up HID Device 
  */
@@ -105,4 +114,10 @@ void hid_device_send_interrupt_message(uint16_t hid_cid, const uint8_t * message
  */
 void hid_device_send_contro_message(uint16_t hid_cid, const uint8_t * message, uint16_t message_len);
 
+/* API_END */
 
+#if defined __cplusplus
+}
+#endif
+
+#endif