Hi,
I was trying to compile lwIP with just LWIP_UDP and LWIP_IPV6 set in lwipopts.h (of all the defines described in [1]), but it failed due to TCP_SLOW_INTERVAL being undeclared in src/api/api_lib.c:737. Sadly I did not know how to open an issue for that in your issue tracker.
Since I'm new to this mailing list a few words about me: I'm one of the core developers behind RIOT [2] and we are currently evaluating our own network stack. To have a comparison (and to have access to the features provided by lwIP) I'm currently in the process of porting lwIP to RIOT.
Kind regards,
Martine Lenders