Make channel so stop doesn't fail; also, test stop.

probe/endpoint/conntrack.go

@@ -94,6 +94,7 @@ func newConntrackFlowWalker(useConntrack bool, args ...string) flowWalker {
 	result := &conntrackWalker{
 		activeFlows: map[int64]flow{},
 		args:        args,
+		quit:        make(chan struct{}),
 	}
 	go result.loop()
 	return result

probe/endpoint/conntrack_internal_test.go

@@ -92,6 +92,7 @@ func TestConntracker(t *testing.T) {
 	}
 
 	flowWalker := newConntrackFlowWalker(true)
+	defer flowWalker.stop()
 
 	// First write out some empty xml for the existing connections
 	ecbw := bufio.NewWriter(existingConnectionsWriter)