Or, if you explicitly need to extract the MAC address see this post UDP With ESP8266 Access Point and for ideas look at the section vis:-
IPaddress = &stat_info->ip;
address = IPaddress->addr;
Serial.print("client= ");
Serial.print(i);
Serial.print(" IP adress is = ");
Serial.print((address));
Serial.print(" with MAC adress is = ");
Serial.print(stat_info->bssid[0],HEX);Serial.print(" ");
Serial.print(stat_info->bssid[1],HEX);Serial.print(" ");
Serial.print(stat_info->bssid[2],HEX);Serial.print(" ");
Serial.print(stat_info->bssid[3],HEX);Serial.print(" ");
Serial.print(stat_info->bssid[4],HEX);Serial.print(" ");
Serial.print(stat_info->bssid[5],HEX);Serial.print(" ");