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().
pcap_setfilter() returns 0 on success and -1 on failure. If -1 is
returned, pcap_geterr() or pcap_perror() may be called with
p as an argument to fetch or display the error text.
pcap(3), pcap_compile(3), pcap_geterr(3)