Add classes Inet4 and Inet6

class Inet6

{

  char m_buffer[IN6_ADDR_SIZE];

  bool str_to_ipv6(const char *str, size_t str_length, CHARSET_INFO *cs);

public:

  // Initialize from a text representation

  Inet6(bool *error, const char *str, size_t length, CHARSET_INFO *cs)

  {

    *error= !str_to_ipv6(str, length, cs);

  }

  // Initialize from a binary representation

  Inet6(bool *error, const char *str, size_t length)

  {

    if (!(*error= length != sizeof(m_buffer)))

      memcpy(m_buffer, str, length);

  }

  Inet6(bool *error, Item *item);

  bool to_binary(String *to) const

  {

    return to->copy(m_buffer, sizeof(m_buffer), &my_charset_bin);

  }

  size_t to_string(char *dst, size_t dstsize) const;

  bool to_string(String *to) const

  {

    to->set_charset(&my_charset_latin1);

    if (to->alloc(INET6_ADDRSTRLEN))

      return true;

    to->length((uint32) to_string((char*) to->ptr(), INET6_ADDRSTRLEN));

    return false;

  }

  bool is_v4compat() const

  {

    static_assert(sizeof(in6_addr) == IN6_ADDR_SIZE, "unexpected in6_addr size");

    return IN6_IS_ADDR_V4COMPAT((struct in6_addr *) m_buffer);

  }

  bool is_v4mapped() const

  {

    static_assert(sizeof(in6_addr) == IN6_ADDR_SIZE, "unexpected in6_addr size");

    return IN6_IS_ADDR_V4MAPPED((struct in6_addr *) m_buffer);

  }

};