[SR-Users] potential PRACK related topos bug

[Juha Heinanen]

Sorry, but it turned out that in calls where B replies first with "183
Session Progress" and which A acknowledges with PRACK request, P1 is not
able to forward the PRACK, but responds with "404 Not found".

I cannot reproduce this in my test environment, because I don't have a
SIP UA that uses Session Progress.  Here is censored debug from
production environment on what happens when P1 receives the PRACK:

https://box.tutpro.com/tmp/prack.debug

-- Juha