pkg/lwip: add mips32 ssize_t fix
pkg/lwip: add mips32 ssize_t fix

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