tests/lwip: add blackpill to BOARD_INSUFFICIENT_MEMORY
tests/lwip: add blackpill to BOARD_INSUFFICIENT_MEMORY

jasonatran/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,OlegHahm/RIOT,ant9000/RIOT,basilfx/RIOT,kaspar030/RIOT,basilfx/RIOT,miri64/RIOT,OTAkeys/RIOT,basilfx/RIOT,authmillenon/RIOT,ant9000/RIOT,kYc0o/RIOT,OlegHahm/RIOT,OlegHahm/RIOT,miri64/RIOT,OTAkeys/RIOT,miri64/RIOT,OTAkeys/RIOT,RIOT-OS/RIOT,OTAkeys/RIOT,RIOT-OS/RIOT,OTAkeys/RIOT,jasonatran/RIOT,OlegHahm/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,jasonatran/RIOT,kYc0o/RIOT,authmillenon/RIOT,jasonatran/RIOT,ant9000/RIOT,RIOT-OS/RIOT,kYc0o/RIOT,ant9000/RIOT,kaspar030/RIOT,kaspar030/RIOT,kaspar030/RIOT,ant9000/RIOT,OlegHahm/RIOT,miri64/RIOT,miri64/RIOT,authmillenon/RIOT,basilfx/RIOT,authmillenon/RIOT,kYc0o/RIOT,basilfx/RIOT,kYc0o/RIOT,jasonatran/RIOT,authmillenon/RIOT