rawapi.txt, api.h, api_lib.c, api_msg.h, api_msg.c, sockets.c, tcp.h, tcp.c, tcp_in.c, init.c, opt.h: rename backlog options with TCP_ prefix, limit the "backlog" parameter in an u8_t, 0 is interpreted as "smallest queue", add documentation in the rawapi.txt file.
#error "If you want to use TCP, TCP_MAXRTX and TCP_SYNMAXRTX must less or equal to 12 (due to tcp_backoff table), so, you have to reduce them in your lwipopts.h"