Hi Olle,
internally function acts the same way as before, so for the above cases it yields the following results:
If there is no IP address in the rtcp attribute - nothing will be changed.
If param has an IPv4 - it will be replaced with the msg source IP address - if only the first argument (flags 0x02, 0x08, 0x10) is passed. Or with the IP address passed as the second argument.
If param contains IPv6 - nothing will be changed.
a possible issue, I have found in my tests, is that it is possible to pass IPv6 as a second argument to the function and it will replace IPv4 address leading to address family mismatch. (e.g c=IN IP4 2001:2345:6789:ABCD:EF01:2345:6789:ABCD) Probably should be mentioned in the nathelper admin guide.