http://arduino.esp8266.com/stable/package_esp8266com_index.json

path packages > esp8266 > hardware > esp8266 > 2.0.0 > tools > sdk > include

typedef void (*freedom_outside_cb_t)(uint8 status);
int wifi_register_send_pkt_freedom_cb(freedom_outside_cb_t cb);
void wifi_unregister_send_pkt_freedom_cb(void);
int wifi_send_pkt_freedom(uint8 *buf, int len, bool sys_seq);