net/portmapper: make PCP/PMP result codes stringers

Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>

net/portmapper/pcpresultcode_string.go

@@ -0,0 +1,37 @@
+// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Code generated by "stringer -type=pcpResultCode -trimprefix=pcpCode"; DO NOT EDIT.
+
+package portmapper
+
+import "strconv"
+
+func _() {
+	// An "invalid array index" compiler error signifies that the constant values have changed.
+	// Re-run the stringer command to generate them again.
+	var x [1]struct{}
+	_ = x[pcpCodeOK-0]
+	_ = x[pcpCodeNotAuthorized-2]
+	_ = x[pcpCodeAddressMismatch-12]
+}
+
+const (
+	_pcpResultCode_name_0 = "OK"
+	_pcpResultCode_name_1 = "NotAuthorized"
+	_pcpResultCode_name_2 = "AddressMismatch"
+)
+
+func (i pcpResultCode) String() string {
+	switch {
+	case i == 0:
+		return _pcpResultCode_name_0
+	case i == 2:
+		return _pcpResultCode_name_1
+	case i == 12:
+		return _pcpResultCode_name_2
+	default:
+		return "pcpResultCode(" + strconv.FormatInt(int64(i), 10) + ")"
+	}
+}