[Devel] t_uac_dlg with nated SIP user agent

[Juha Heinanen]

if a sip ua is behind nat, uac fifo accepts the actual destination uri
on the fourth line of the request:

	:t_uac:[file] EOL
	method EOL
	r-uri EOL 
	dst EOL 	// ("." if no outbound server used
        ...

and sends the request to that uri instead of the r-uri on the previous
line.

if the request happens to be invite, t_uac_dlg needs to send ack after
receiving 200 ok from the sip ua.  that ack, however, is NOT sent to dst
uri, but according to contact uri of 200 ok.

in order for that to work, 200 ok should be either processed by a
t_on_reply block or t_uac should also send the ack to dst uri (if not
empty) instead of contact uri.

so the options are either to somehow pass t_on_reply block number to
t_uac_dialog via the fifo request or modify t_uac so that also ack gets
sent to dst uri (if present).  i personally would prefer the latter
choice.

-- juha