LWIP_DNS_API_HOSTENT_STORAGE macro

LWIP_DNS_API_HOSTENT_STORAGE: if set to 0 (default), lwip_gethostbyname() returns the same global variabe for all calls (in all threads). When set to 1, your port should provide a function struct hostent* sys_thread_hostent( struct hostent* h); which have to do a copy of "h" and return a pointer ont the "per-thread" copy.