fix: convert dns_hosts from list to option format in UCI

tachyon/files/usr/lib/config/migration.uc

@@ -1285,10 +1285,34 @@ function migrate_http_connection_urls(ctx) {
     }
 }
 
+function migrate_dns_hosts_to_option(ctx) {
+    let raw = object_or_empty(ctx.model.settings)["dns_hosts"];
+    if (raw == null)
+        return;
+
+    if (type(raw) != "array")
+        return;
+
+    let entries = [];
+    for (let value in raw) {
+        value = as_string(value);
+        if (value != "")
+            push(entries, value);
+    }
+
+    if (length(entries) == 0) {
+        delete_option(ctx, ctx.model.settings, "dns_hosts");
+        return;
+    }
+
+    set_option(ctx, ctx.model.settings, "dns_hosts", join("\n", entries));
+}
+
 const MIGRATIONS = [
     { id: "interface_sections", run: migrate_interface_sections },
     { id: "enable_component_checks", run: migrate_enable_component_checks },
-    { id: "http_connection_urls", run: migrate_http_connection_urls }
+    { id: "http_connection_urls", run: migrate_http_connection_urls },
+    { id: "dns_hosts_to_option", run: migrate_dns_hosts_to_option }
 ];
 
 function apply_migrations(ctx) {