Pull in soft assert change in PJSIP
Merge pull request #276 from Metaswitch/issue273

[No reviewer] Pull in soft assert change in PJSIP
Fix UT compile failures (caused by #including PJSIP headers without surrounding extern "C" directive)
Merge pull request #277 from Metaswitch/issue273

[No reviewer] Fix UT compile failures (caused by #including PJSIP headers without surrounding extern "C" directive)