logging: add a Close function to the Tracer (#4298)

* logging: add a Close function to the Tracer

* close the Tracer when the Transport is closed

logging/tracer.go

@@ -8,6 +8,7 @@ type Tracer struct {
 	SentVersionNegotiationPacket func(_ net.Addr, dest, src ArbitraryLenConnectionID, _ []VersionNumber)
 	DroppedPacket                func(net.Addr, PacketType, ByteCount, PacketDropReason)
 	Debug                        func(name, msg string)
+	Close                        func()
 }
 
 // NewMultiplexedTracer creates a new tracer that multiplexes events to multiple tracers.
@@ -47,5 +48,12 @@ func NewMultiplexedTracer(tracers ...*Tracer) *Tracer {
 				}
 			}
 		},
+		Close: func() {
+			for _, t := range tracers {
+				if t.Close != nil {
+					t.Close()
+				}
+			}
+		},
 	}
 }