net_short
#define native_long(x) (htonl((net_short(x) << 16) + \
net_short((unsigned char *)(x) + 2)))
#define get_iplen(x) net_short((unsigned char *)(x) + 2)
#define get_ipoff(x) net_short((unsigned char *)(x) + 6)
#define get_sport(x) net_short(x)
#define get_dport(x) net_short((unsigned char *)(x) + 2)