I have never used it myself. I just wanted to help this one mailing list post, but of course, this commit is broken.
I just looked into the path module how it's done there, and there exists a struct for different transports:
```const static char *proto_strings[] = { [PROTO_TCP] = "%3Btransport%3Dtcp", [PROTO_TLS] = "%3Btransport%3Dtls", [PROTO_SCTP] = "%3Btransport%3Dsctp", [PROTO_WS] = "%3Btransport%3Dws", [PROTO_WSS] = "%3Btransport%3Dws", };```
This gets appended to the received param if needed. Then a Path header looks like this:
```Path: sip:1.2.3.4;lr;received=sip:4.3.2.1:49194%3Btransport%3Dtcp.```
Unfortunately I'm not able to implement that for the nathelper module as my C knowledge is limited to doing such trivial stuff like the commit above.