lwip/sntp: Added extern "C"

so that sntp_set_time_sync_notification_cb can be used from c++

Signed-off-by: Konstantin Kondrashov <konstantin@espressif.com>

Merges: https://github.com/espressif/esp-idf/pull/3700

components/lwip/include/apps/sntp/sntp.h

@@ -15,6 +15,10 @@
 #ifndef __SNTP_H__
 #define __SNTP_H__
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /*
  * The time update takes place in the sntp_sync_time() function.
  * The user has the ability to redefine this function in order
@@ -116,4 +120,8 @@ void sntp_set_sync_status(sntp_sync_status_t sync_status);
  */
 void sntp_set_time_sync_notification_cb(sntp_sync_time_cb_t callback);
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif // __SNTP_H__