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/doc.go

@@ -0,0 +1,29 @@
+// Package wgctrl enables control of WireGuard devices on multiple platforms.
+//
+// For more information on WireGuard, please see https://www.wireguard.com/.
+//
+//   go get golang.zx2c4.com/wireguard/wgctrl
+//
+//
+// Overview
+//
+// wgctrl can control multiple types of WireGuard devices, including:
+//
+//   - Linux kernel module devices, via generic netlink
+//   - userspace devices (e.g. wireguard-go), via the userspace configuration protocol
+//     - both UNIX-like and Windows operating systems are supported
+//   - **Experimental:** OpenBSD kernel module devices, via ioctl interface
+//     See <https://git.zx2c4.com/wireguard-openbsd/about/> for details. Specify
+//     environment variable WGCTRL_OPENBSD_KERNEL=1 to enable this interface.
+//
+// As new operating systems add support for in-kernel WireGuard implementations,
+// this package should also be extended to support those native implementations.
+//
+// If you are aware of any efforts on this front, please file an issue:
+// https://github.com/WireGuard/wgctrl-go/issues/new.
+//
+// This package implements WireGuard configuration protocol operations, enabling
+// the configuration of existing WireGuard devices. Operations such as creating
+// WireGuard devices, or applying IP addresses to those devices, are out of scope
+// for this package.
+package wgctrl // import "golang.zx2c4.com/wireguard/wgctrl"