[Core] JB: small fixes and adjusments

[jchavanton]

• [Core] JB: if the jitter buffer size is above the its max size, we force accelerate

• [Core] JB: proper handling of seq roll-over

• [Core] JB: fix seq decrement

These fixes and the adjustment were thoroughly tested, they were found while testing the packet relay metrics. #2292

A/B testing with 100 sessions and no artificial jitter, to make sure everything is working well under normal conditions.

• less packets are replaced by PLC or simply skipped with the default JB
• less delays is introduced

EJB : more elastic jitter buffer

The packet relay metrics are still not ready for merge but I am able to use them to precisely monitor the jitter buffer in production.

---

Here is one report of real traffic facing jitter, I selected it randomly from production traffic.
We can use it as a source of validation evidence.
Configuration:

<action application="set" data="rtp_jitter_buffer_accelerate=true"/>
<action application="set" data="jitterbuffer_msec=20:1200"/>

End of call report:

{
  "rp": {
    "call_id_in": "rt342cma1dgelvphc5pb",
    "call_id_out": "c454bbd8-4e26-4049-85bb-20569a0b2990",
    "report": {
      "in": {
        "ssrc": "0x95262C82",
        "remote_socket": "172.11.61.245:18550",
        "local_socket": "172.11.61.245:35930",
        "codec": "opus",
        "count": 43181,   // ~15 minutes call
        "plc": 732   //  1.6% PLC
      },
      "out": {
        "ssrc": "0xA95A90EE",
        "remote_socket": "172.11.50.19:34402",
        "local_socket": "172.11.61.245:13842",
        "codec": "PCMU",
        "count": 43181,
        "max_ms": 1060,   // this is the maximum time spent by any packet inside FS, we can see close to matching the JB max size.
        "avg_ms": 74.57   // this is the average time spent by any packet inside FS
      }
    }
  },
  "jb": {
    "in_call_id": "rt342cma1dgelvphc5pb",
    "out_call_id": "c454bbd8-4e26-4049-85bb-20569a0b2990",
    "jb": {
      "size_max_ms": 1220,   // we can see that the maximum jitter buffer size was respected
      "size_est_ms": 20,
      "acceleration_ms": 13680,
      "expand_ms": 13580,
      "fast_acceleration_ms": 0,
      "forced_acceleration_ms": 60,   // at one point the jitter buffer was above its max size
      "jitter_max_ms": 140,   // very high jitter was seen during that call
      "jitter_est_ms": 8,   // near the end there was not that much jitter
      "reset": 7,
      "reset_too_big": 0
    }
  }
}

[signalwire-ci]

Unit-tests failed: https://public-artifacts.signalwire.cloud/drone/signalwire/freeswitch/1596/artifacts.html

[signalwire-ci]

Scan-build found bugs: https://public-artifacts.signalwire.cloud/drone/signalwire/freeswitch/1596/index.html

[jchavanton]

REPLACED WITH

#2337