Cannot create sockets when using `setdest` for transport mode `un` (UDP with one socket per call)

[ewittingen]

When running a sipp scenario which contains a setdest action (see https://sipp.readthedocs.io/en/latest/scenarios/actions.html#setdest) with transport mode "UDP with one socket per call" using ./sipp -t un ... it crashes with the error "Cannot create socket" when starting the first call. When removing the setdest action, this error does not occur and calls can be performed without any errors.

This error even happens when the contents of setdest are the same as the original destination passed to the cli:

<nop>
  <action>
    <setdest host="[remote_host]" port="[remote_port]" protocol="[transport]" />
  </action>
</nop>

When setting the transport mode to "UDP with one socket" or "TCP with one socket per call" whilst keeping setdest in the scenario, the "Cannot create socket" error does not occur either.

So it appears to only be an issue with setdest and the un transport mode.