I have submitted a patch for a GPL'd project and now a third-party wants to include this patch in a product. They have asked me what license my patch uses.
Does my patch have to adopt the GPL license? Or I can choose an alternative one?
If you are using the original code base for which the patch was built in ANY way, you must use the GPL license.
If your patch is fully independent (which patch that is fully independent is not really a "patch") and can stand on its own two feet, then use whatever licensing you want.
This may help clarify http://www.sitepoint.com/public-license-explained/