tracing: log_p2p_connections.bt example

A bpftrace script that logs information from the
net:*_connection tracepoints.

I've tested this script with bpftrace version 0.14.1 and v0.20.2.

contrib/tracing/README.md

@@ -335,4 +335,25 @@ $ python3 contrib/tracing/mempool_monitor.py $(pidof bitcoind)
  │ 13:10:32Z added c78e87be86c828137a6e7e00a177c03b52202ce4c39029b99904c2a094b9da87 with feerate 11.00 sat/vB (1562 sat, 142 vbytes)                                            │
  │                                                                                                                                                                              │
  └──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
+
+### log_p2p_connections.bt
+
+A `bpftrace` script to log information about opened, closed, misbehaving, and
+evicted P2P connections. Uses the `net:*_connection` tracepoints.
+
+```bash
+$ bpftrace contrib/tracing/log_p2p_connections.bt
+```
+
+This should produce an output similar to the following.
+
+```bash
+Attaching 6 probes...
+Logging opened, closed, misbehaving, and evicted P2P connections
+OUTBOUND conn to 127.0.0.1:15287: id=0, type=block-relay-only, network=0, total_out=1
+INBOUND conn from 127.0.0.1:45324: id=1, type=inbound, network=0, total_in=1
+MISBEHAVING conn id=1, score_before=0, score_increase=20, message='getdata message size = 50001', threshold_exceeded=false
+CLOSED conn to 127.0.0.1:15287: id=0, type=block-relay-only, network=0, established=1231006505
+EVICTED conn to 127.0.0.1:45324: id=1, type=inbound, network=0, established=1612312312
+...
 ```