Here is some code that I used for testing. You'll need some dependencies:
A link layer reflector driver that shorts the link. Note that you need to have the same scr and dst address when doing such kind of loopback. To avoid running into the IPv6 loopback, there is a small workaround in that branch which takes out some loopback checks if LOOPBACK_MODE is not defined
l2_reflector branch
Attention! Using the above application might cause hard faults on a board. In that case you might want to apply the following patch on your master to increase the stack size of the main thread patch file