I am gound flags for rtpproxy_manage(which help external (behind NAT) UA registerd on Kamailio call to Echo() test extension on Asterisk - it is "cwie". But for Peer-to-Peerm, registered on Kamailio and working though Asterisk dialplan, it must be rtpproxy_manage("cwii").
Thanks to author of this example of kamailio.cfg https://github.com/xlab1/sipfe_kamailio/blob/master/kamailio.cfg
And from Kamailio documentation for rtpproxy_offer([flags [, ip_address]]):
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*c* - flags to change the session-level SDP connection (c=) IP if media-description also includes connection information. -
*w* - flags that for the UA from which message is received, support symmetric RTP must be forced.
Hope I am understand what I do =) Thank you all for speaking with me! I'll be back... ASAP