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
Closes: IDF-236 Closes: https://github.com/espressif/esp-idf/pull/1668 Closes: https://github.com/espressif/esp-idf/pull/4103