[OpenSIPS-Devel] [OpenSIPS/opensips] a0bbd6: [b2b_logic] fix crash on tracing expired b2b tuples

[Bogdan Andrei IANCU]

  Branch: refs/heads/3.4
  Home:   https://github.com/OpenSIPS/opensips
  Commit: a0bbd60c366ed0137ee432ea2f23c0a1f75019c4
      https://github.com/OpenSIPS/opensips/commit/a0bbd60c366ed0137ee432ea2f23c0a1f75019c4
  Author: Bogdan-Andrei Iancu <bogdan at opensips.org>
  Date:   2023-06-30 (Fri, 30 Jun 2023)

  Changed paths:
    M context.c
    M context.h
    M modules/b2b_logic/b2b_logic.c

  Log Message:
  -----------
  [b2b_logic] fix crash on tracing expired b2b tuples

When a tuple expires via timer, be sure to provide a processing context, otherwise the tracer (if enabled) will simply crash.
As part of the fix, two new helper functions were added for pushing and poping new processing contexts - these are to be reused by some prev similar fix on uac_registrant.
Related to #3110
Many thanks to @vtzan for helping with the troubleshooting and testing

(cherry picked from commit 2a3eb1e2a8e609b6b7b37074c1d1fd4dffc76f5e)