Check that there is no dangling call in PBX (moved)

Moved to ​https://docs.pjsip.org/en/latest/specific-guides/audio-troubleshooting/checks/dangling_pbx_call.html

Sometimes, when pjsua crashed for some reason, the call is still left active in the PBX. When subsequent pjsua application is started, this new application instance will receive two RTP streams simultaneously from the PBX: once from current call, and one from the dangling call. This would definitely cause audio breakup problem in pjsua.

This happens because pjsua by default will use UDP port 4000 for the RTP port, so both calls (the dangling and active call in the PBX) will send to the same port 4000 of pjsua.