What’s the news value of this? LWIP is the most popular embedded network stack and has been around for ages. It also is awful to use and riddled with undocumented issues (in my experience, anyway)
Plugging in a new TCP congestion control scheme was also straightforward.
the biggest problem with lwip is the documentation. you have doxygen API docs that tell you exactly what the interfaces are (and not much more than the reading the header filed does), you have a few pages of "how to ..." and higher level background. but often it's slightly bit rotted, subtly hasn't kept up with design changes. so it's difficult to learn - you effectively have to thoroughly read the code to get the big picture. and if you make a mistake in handling your application callbacks, you can easily leak buffers or create other problems. it's not "awful to use", it's actually very simple - once you understand it, which is seriously hampered by truly lacking documentation.
the second issue is that the SoC vendors inevitably pay some overseas contractor to do the port and MAC/PHY drivers and example code, just like another [1] comment describes. that's where a lot of the instability and bugs come in. it's not lwip, it's the port that sucks.
It's allowed to repost "classic" stuff on HN as long as it isn't too frequent.