[Serusers] How to check receive port in ser.cfg

[serusers at jtoga.org]

We have a 0.9.X setup that works fine and have set up the system to
listen on multiple ports with the following

listen=udp:xx.xx.xx.xx:5060  udp:xx.xx.xx.xx:5062

The problem is that when setting the "record route" we want to use the
port that the message came in on rather than
simply a static value...

   record_route_preset("xx.xx.xx.xx:5060;nat=yes");

Something like

if (receive port == 5060) {
   record_route_preset("xx.xx.xx.xx:5060;nat=yes");
}
else if (receive port ==5062) {
   record_route_preset("xx.xx.xx.xx:5062;nat=yes");
};

What can we check in ser.cfg?

Thanks in advance.