pcap_snapshot - get the snapshot length
#include <pcap/pcap.h>
int pcap_snapshot(pcap_t *p);
pcap_snapshot() returns the snapshot length specified when
  pcap_set_snaplen(3) or pcap_open_live(3) was called, for a live
  capture, or the snapshot length from the capture file, for a ``savefile''.
It must not be called on a pcap descriptor created by
    pcap_create(3) that has not yet been activated by
    pcap_activate(3).
pcap_snapshot() returns the snapshot length on success and
  PCAP_ERROR_NOT_ACTIVATED if called on a capture handle that has been
  created but not activated.