feat(protonvpn): port forwarding support with NAT-PMP (#1543)

Co-authored-by: Nicholas Xavier <nicho@nicho.dev>

internal/natpmp/natpmp_test.go

@@ -0,0 +1,20 @@
+package natpmp
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_New(t *testing.T) {
+	t.Parallel()
+
+	expectedClient := &Client{
+		serverPort:   5351,
+		initialRetry: 250 * time.Millisecond,
+		maxRetries:   9,
+	}
+	client := New()
+	assert.Equal(t, expectedClient, client)
+}