1. Move htonl() etc. from <arpa/inet.h> to <netinet/in.h> (which
<arpa/inet.h> includes).
The htonl(), htons(), ntohl(), and ntohs() functions shall be
available as described in <arpa/inet.h>. Inclusion of the
<netinet/in.h> header may also make visible all symbols from
<arpa/inet.h>.
- POSIX
2. Define IN6_IS_ADDR_LOOPBACK() and IN6_IS_ADDR_V4MAPPED()