This field is an exact copy of `ndpi_flow_struct->detected_protocol_stack[2]`: * at the very beginning of packet dissection, the value saved in `flow->detected_protocol_stack` is copied in `packet->detected_protocol_stack` (via `ndpi_detection_process_packet()` -> `ndpi_init_packet_header()`) * every time we update `flow->detected_protocol_stack` we update `packet->detected_protocol_stack` too (via `ndpi_int_change_protocol()` -> `ndpi_int_change_packet_protocol()`) These two fields are always in sync: keeping the same value in two different places is useless.