net/portmapper: make PCP/PMP result codes stringers

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

net/portmapper/pmpresultcode_string.go

@@ -0,0 +1,32 @@
+// 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=pmpResultCode -trimprefix=pmpCode"; 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[pmpCodeOK-0]
+	_ = x[pmpCodeUnsupportedVersion-1]
+	_ = x[pmpCodeNotAuthorized-2]
+	_ = x[pmpCodeNetworkFailure-3]
+	_ = x[pmpCodeOutOfResources-4]
+	_ = x[pmpCodeUnsupportedOpcode-5]
+}
+
+const _pmpResultCode_name = "OKUnsupportedVersionNotAuthorizedNetworkFailureOutOfResourcesUnsupportedOpcode"
+
+var _pmpResultCode_index = [...]uint8{0, 2, 20, 33, 47, 61, 78}
+
+func (i pmpResultCode) String() string {
+	if i >= pmpResultCode(len(_pmpResultCode_index)-1) {
+		return "pmpResultCode(" + strconv.FormatInt(int64(i), 10) + ")"
+	}
+	return _pmpResultCode_name[_pmpResultCode_index[i]:_pmpResultCode_index[i+1]]
+}