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/github.com/mdlayher/netlink/debug.go

@@ -0,0 +1,69 @@
+package netlink
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"strconv"
+	"strings"
+)
+
+// Arguments used to create a debugger.
+var debugArgs []string
+
+func init() {
+	// Is netlink debugging enabled?
+	s := os.Getenv("NLDEBUG")
+	if s == "" {
+		return
+	}
+
+	debugArgs = strings.Split(s, ",")
+}
+
+// A debugger is used to provide debugging information about a netlink connection.
+type debugger struct {
+	Log   *log.Logger
+	Level int
+}
+
+// newDebugger creates a debugger by parsing key=value arguments.
+func newDebugger(args []string) *debugger {
+	d := &debugger{
+		Log:   log.New(os.Stderr, "nl: ", 0),
+		Level: 1,
+	}
+
+	for _, a := range args {
+		kv := strings.Split(a, "=")
+		if len(kv) != 2 {
+			// Ignore malformed pairs and assume callers wants defaults.
+			continue
+		}
+
+		switch kv[0] {
+		// Select the log level for the debugger.
+		case "level":
+			level, err := strconv.Atoi(kv[1])
+			if err != nil {
+				panicf("netlink: invalid NLDEBUG level: %q", a)
+			}
+
+			d.Level = level
+		}
+	}
+
+	return d
+}
+
+// debugf prints debugging information at the specified level, if d.Level is
+// high enough to print the message.
+func (d *debugger) debugf(level int, format string, v ...interface{}) {
+	if d.Level >= level {
+		d.Log.Printf(format, v...)
+	}
+}
+
+func panicf(format string, a ...interface{}) {
+	panic(fmt.Sprintf(format, a...))
+}