Fail to compile with esp-idf release/v4.2

[mathiasbredholt]

I issued a pull request to fix this issue: espressif/esp-idf#5900
In the mean time change the file esp-idf/components/lwip/port/esp32/include/netdb.h to:

#ifdef __cplusplus
extern "C" {
#endif

int getnameinfo(const struct sockaddr *addr, socklen_t addrlen,
                char *host, socklen_t hostlen,
                char *serv, socklen_t servlen, int flags);

#ifdef __cplusplus
}
#endif

[mathiasbredholt]

The mentioned pull request has been merged into master espressif/esp-idf@8a10292