pcap_setfilter - set the filter
#include <pcap/pcap.h>
int pcap_setfilter(pcap_t *p, struct bpf_program *fp);
pcap_setfilter() is used to specify a filter program. fp is a
pointer to a bpf_program struct, usually the result of a call to
pcap_compile(3).
pcap_setfilter() returns 0 on success and PCAP_ERROR on failure.
If PCAP_ERROR is returned, pcap_geterr(3) or
pcap_perror(3) may be called with p as an argument to fetch or
display the error text.