I have added extra logs sctrings and found. This happens because sockaddr_union `from` contains port number 5060 https://github.com/kamailio/kamailio/blob/master/src/core/forward.h#L188-L19...
This port assigned from "dest_info* dst" https://github.com/kamailio/kamailio/blob/master/src/core/forward.h#L174
This struct passed into msg_send_buffer here https://github.com/kamailio/kamailio/blob/master/src/core/forward.h#L117
Need to find why for ACK delivery used not socket where WebRTC client registered, but used socket bound to port 5060.