pcap_lookupnet - find the IPv4 network number and netmask for a device
int pcap_lookupnet(const char *device, bpf_u_int32 *netp,
bpf_u_int32 *maskp, char *errbuf);
pcap_lookupnet() is used to determine the IPv4 network number and mask
associated with the network device device. Both netp and
maskp are bpf_u_int32 pointers.
pcap_lookupnet() returns 0 on success and PCAP_ERROR on failure.
If PCAP_ERROR is returned, errbuf is filled in with an
appropriate error message. errbuf is assumed to be able to hold at
least PCAP_ERRBUF_SIZE chars.