registrar: adding tcpconn_id to xavp_cfg

[jchavanton]

Pre-Submission Checklist

• Commit message has the format required by CONTRIBUTING guide
• Commits are split per component (core, individual modules, libs, utils, ...)
• Each component has a single commit (if not, squash them into one commit)
• No commits to README files for modules (changes must be done to docbook files
  in doc/ subfolder, the README file is autogenerated)

Type Of Change

• New feature (non-breaking change which adds new functionality)

Checklist:

• Tested changes locally

Description

This is adding the variable tcpconn_id to xavp_cfg

When using Kamailio as a "mid registrar", we need to save the contact in the reply-route (once we have the confirmation from the registrar), one problem I faced was that the tcpconid was the one of the response message coming from the registrar.
I needed a way to save the one of the original request message.

mid registrar config example where we need/use the tcpconnid

modparam("registrar", "xavp_cfg", "reg")

route[REGISTER] {
    ...
    t_on_reply("ON_REPLY_REGISTER");
    $xavp(reg=>tcpconn_id) = $conid; // set the TCP connection id to be saved on the reply
   ....
}

onreply_route[ON_REPLY_REGISTER] {
        if (t_check_status("200")) {
                if (is_present_hf("Expires") && $hdr(Expires) == "0") {
                        xinfo("[ON_REPLY_REGISTER][$rm][$ci] registrar remove[$var(ret)]\n");
                        $var(ret) = unregister("location", "$tu");
                } else {
                        xinfo("[ON_REPLY_REGISTER][$rm][$ci] registrar save[$var(ret)]\n");
                        $var(ret) = save("location", "0x02");
                }
        }
}

route[INVITE] {
    ...
    if(reg_fetch_contacts("location", "$ru", "caller"))  {
         if(!tcp_conid_alive("$var(conid)")) {
                 xinfo("[RELAY][$ci] using tcp connection inactive [$var(conid)] suspend/push\n");
                 route(PUSH_SUSPEND);
         } else {
                  xinfo("[RELAY][$ci] using tcp connection [$var(conid)]\n");
         }
     }
     ...
}

[miconda]

Thanks!