ECN+ Implementation

[Pavan Vachhani]

Hi,
I am trying to implement ECN+ (rfc5562 <https://tools.ietf.org/html/rfc5562>)
in FreeBSD.
I am not able to figure out the code where SYN and SYN+ACK is sent and
received.
Please guide me to correct part of code. It was looking into tcp_input.c
and tcp_output.c but couldn't get it for sure.
Sorry for simple questions, I am a beginner.

Thanks in advance.