Wireguard support for Mullvad and Windscribe (#565)

- `internal/wireguard` client package with unit tests
- Implementation works with kernel space or user space if unavailable
- `WIREGUARD_PRIVATE_KEY`
- `WIREGUARD_ADDRESS`
- `WIREGUARD_PRESHARED_KEY`
- `WIREGUARD_PORT`
- `internal/netlink` package used by `internal/wireguard`

internal/wireguard/log_test.go

@@ -0,0 +1,23 @@
+package wireguard
+
+import (
+	"testing"
+
+	"github.com/golang/mock/gomock"
+)
+
+func Test_makeDeviceLogger(t *testing.T) {
+	t.Parallel()
+
+	ctrl := gomock.NewController(t)
+
+	logger := NewMockLogger(ctrl)
+
+	deviceLogger := makeDeviceLogger(logger)
+
+	logger.EXPECT().Debug("test 1")
+	deviceLogger.Verbosef("test %d", 1)
+
+	logger.EXPECT().Error("test 2")
+	deviceLogger.Errorf("test %d", 2)
+}