Use PMTUD to set the MTU to the VPN interface

- Add `VPN_PMTUD` option enabled by default
- One can revert to use `VPN_PMTUD=off` to disable the new PMTUD mechanism

internal/vpn/wireguard.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 
 	"github.com/qdm12/gluetun/internal/configuration/settings"
+	"github.com/qdm12/gluetun/internal/models"
 	"github.com/qdm12/gluetun/internal/provider"
 	"github.com/qdm12/gluetun/internal/provider/utils"
 	"github.com/qdm12/gluetun/internal/wireguard"
@@ -16,11 +17,11 @@ import (
 func setupWireguard(ctx context.Context, netlinker NetLinker,
 	fw Firewall, providerConf provider.Provider,
 	settings settings.VPN, ipv6Supported bool, logger wireguard.Logger) (
-	wireguarder *wireguard.Wireguard, serverName string, canPortForward bool, err error,
+	wireguarder *wireguard.Wireguard, connection models.Connection, err error,
 ) {
-	connection, err := providerConf.GetConnection(settings.Provider.ServerSelection, ipv6Supported)
+	connection, err = providerConf.GetConnection(settings.Provider.ServerSelection, ipv6Supported)
 	if err != nil {
-		return nil, "", false, fmt.Errorf("finding a VPN server: %w", err)
+		return nil, models.Connection{}, fmt.Errorf("finding a VPN server: %w", err)
 	}
 
 	wireguardSettings := utils.BuildWireguardSettings(connection, settings.Wireguard, ipv6Supported)
@@ -31,13 +32,13 @@ func setupWireguard(ctx context.Context, netlinker NetLinker,
 
 	wireguarder, err = wireguard.New(wireguardSettings, netlinker, logger)
 	if err != nil {
-		return nil, "", false, fmt.Errorf("creating Wireguard: %w", err)
+		return nil, models.Connection{}, fmt.Errorf("creating Wireguard: %w", err)
 	}
 
 	err = fw.SetVPNConnection(ctx, connection, settings.Wireguard.Interface)
 	if err != nil {
-		return nil, "", false, fmt.Errorf("setting firewall: %w", err)
+		return nil, models.Connection{}, fmt.Errorf("setting firewall: %w", err)
 	}
 
-	return wireguarder, connection.ServerName, connection.PortForward, nil
+	return wireguarder, connection, nil
 }