control/controlclient: fix copy/paste-o in debug knob accessor

Introduced in a975e86bb8.

Only affected TS_DEBUG_* env users.

control/controlclient/direct.go

@@ -800,7 +800,7 @@ func envBool(k string) bool {
 	if e == "" {
 		return false
 	}
-	v, err := strconv.ParseBool(os.Getenv("TS_DEBUG_NETMAP"))
+	v, err := strconv.ParseBool(e)
 	if err != nil {
 		panic(fmt.Sprintf("invalid non-bool %q for env var %q", e, k))
 	}