add WG_SERVER_MTU to config.js, enable MTU only if mtu is specified

src/config.js

@@ -13,6 +13,7 @@ module.exports.WG_PATH = process.env.WG_PATH || '/etc/wireguard/';
 module.exports.WG_DEVICE = process.env.WG_DEVICE || 'eth0';
 module.exports.WG_HOST = process.env.WG_HOST;
 module.exports.WG_PORT = process.env.WG_PORT || '51820';
+module.exports.WG_SERVER_MTU = process.env.WG_SERVER_MTU;
 module.exports.WG_CONFIG_PORT = process.env.WG_CONFIG_PORT || process.env.WG_PORT || '51820';
 module.exports.WG_MTU = process.env.WG_MTU || null;
 module.exports.WG_PERSISTENT_KEEPALIVE = process.env.WG_PERSISTENT_KEEPALIVE || '0';

src/lib/WireGuard.js

@@ -108,7 +108,7 @@ module.exports = class WireGuard {
 PrivateKey = ${config.server.privateKey}
 Address = ${config.server.address}/24
 ListenPort = ${WG_PORT}
-MTU = ${WG_SERVER_MTU}
+${WG_SERVER_MTU ? `MTU = ${WG_SERVER_MTU}` : ''}
 PreUp = ${WG_PRE_UP}
 PostUp = ${WG_POST_UP}
 PreDown = ${WG_PRE_DOWN}