Wakaama example on lwIP IPv4 and IPv6


I have been able to extend the Wakaama example to build for lwIP sock IPv4 and IPv6 [1]. This extension builds on the great recent work by @gchorcht, @wosym, and others to enable IPv4 for lwIP.

I decided to just post a notice rather than create a WIP PR. I had to #ifdef-out code related to netif functions, so an implementation for lwIP, as @miri64 has started with #9343, would be useful first. Also, I'm not sure how extensively we want to start bringing in IPv4 for examples. I had to add several #ifdefs for things like `ipvN_addr_equal()`.

At any rate, the example should provide some food for thought on the issues around supporting both IP versions. It's also valuable to me to demo RIOT running LwM2M on IPv4!


[1] https://github.com/kb2ma/RIOT/tree/wakaama/lwip_ipv4_poc