settings: move dynamic dns to network

and add tests

src/network.js

@@ -3,10 +3,14 @@
 exports = module.exports = {
     getBlocklist,
     setBlocklist,
+
+    getDynamicDns,
+    setDynamicDns,
 };
 
 const assert = require('assert'),
     BoxError = require('./boxerror.js'),
+    cron = require('./cron.js'),
     ipaddr = require('ipaddr.js'),
     path = require('path'),
     paths = require('./paths.js'),
@@ -53,3 +57,15 @@ async function setBlocklist(blocklist, auditSource) {
     const [error] = await safe(shell.promises.sudo('setBlocklist', [ SET_BLOCKLIST_CMD ], {}));
     if (error) throw new BoxError(BoxError.IPTABLES_ERROR, `Error setting blocklist: ${error.message}`);
 }
+
+async function getDynamicDns() {
+    const enabled = await settings.get(settings.DYNAMIC_DNS_KEY);
+    return enabled ? !!enabled : false; // db holds string values only
+}
+
+async function setDynamicDns(enabled) {
+    assert.strictEqual(typeof enabled, 'boolean');
+
+    await settings.set(settings.DYNAMIC_DNS_KEY, enabled ? 'enabled' : ''); // db holds string values only
+    cron.dynamicDnsChanged(enabled);
+}