migrate to golang.zx2c4.com/wireguard/wgctrl (#239)

* migrate to golang.zx2c4.com/wireguard/wgctrl

This commit introduces the usage of wgctrl.
It avoids the usage of exec calls of the wg command
and parsing the output of `wg show`.

Signed-off-by: leonnicolas <leonloechner@gmx.de>

* vendor wgctrl

Signed-off-by: leonnicolas <leonloechner@gmx.de>

* apply suggestions from code review

Remove wireguard.Enpoint struct and use net.UDPAddr for the resolved
endpoint and addr string (dnsanme:port) if a DN was supplied.

Signed-off-by: leonnicolas <leonloechner@gmx.de>

* pkg/*: use wireguard.Enpoint

This commit introduces the wireguard.Enpoint struct.
It encapsulates a DN name with port and a net.UPDAddr.
The fields are private and only accessible over exported Methods
to avoid accidental modification.

Also iptables.GetProtocol is improved to avoid ipv4 rules being applied
by `ip6tables`.

Signed-off-by: leonnicolas <leonloechner@gmx.de>

* pkg/wireguard/conf_test.go: add tests for Endpoint

Signed-off-by: leonnicolas <leonloechner@gmx.de>

* cmd/kg/main.go: validate port range

Signed-off-by: leonnicolas <leonloechner@gmx.de>

* add suggestions from review

Signed-off-by: leonnicolas <leonloechner@gmx.de>

* pkg/mesh/mesh.go: use Equal func

Implement an Equal func for Enpoint and use it instead of comparing
strings.

Signed-off-by: leonnicolas <leonloechner@gmx.de>

* cmd/kgctl/main.go: check port range

Signed-off-by: leonnicolas <leonloechner@gmx.de>

* vendor

Signed-off-by: leonnicolas <leonloechner@gmx.de>

vendor/golang.zx2c4.com/wireguard/wgctrl/internal/wginternal/client.go

@@ -0,0 +1,21 @@
+package wginternal
+
+import (
+	"errors"
+	"io"
+
+	"golang.zx2c4.com/wireguard/wgctrl/wgtypes"
+)
+
+// ErrReadOnly indicates that the driver backing a device is read-only. It is
+// a sentinel value used in integration tests.
+// TODO(mdlayher): consider exposing in API.
+var ErrReadOnly = errors.New("driver is read-only")
+
+// A Client is a type which can control a WireGuard device.
+type Client interface {
+	io.Closer
+	Devices() ([]*wgtypes.Device, error)
+	Device(name string) (*wgtypes.Device, error)
+	ConfigureDevice(name string, cfg wgtypes.Config) error
+}

vendor/golang.zx2c4.com/wireguard/wgctrl/internal/wginternal/doc.go

@@ -0,0 +1,5 @@
+// Package wginternal contains shared internal types for wgctrl.
+//
+// This package is internal-only and not meant for end users to consume.
+// Please use package wgctrl (an abstraction over this package) instead.
+package wginternal