OpenSIPS doesn't add 'recevied' parameter to Via in case that rport is present in original Via, but the address in Via is the same with src_ip.
This behavior brakes RFC 3581:
4. Server Behavior
The server behavior specified here affects the transport processing
defined in Section 18.2 of SIP .
When a server compliant to this specification (which can be a proxy
or UAS) receives a request, it examines the topmost Via header field
value. If this Via header field value contains an "rport" parameter
with no value, it MUST set the value of the parameter to the source
port of the request. This is analogous to the way in which a server
will insert the "received" parameter into the topmost Via header
field value. In fact, the server MUST insert a "received" parameter
containing the source IP address that the request came from, even if
it is identical to the value of the "sent-by" component. Note that
this processing takes place independent of the transport protocol.