Pull in libpcap's new DLTs

Pull in libpcap's new DLTs

This commit targets using system net/bpf.h in libpcap instead of
libpcap's own pcap-bpf.h; mainly to make following code compile:
  #include <pcap.h>
  #include <net/bpf.h>

Reported-by: hasso@
Note:
As of this commit DLT_PFSYNC is changed to 18.  The original define
conflicts with libpcap's define and it looks like both libpcap,
NetBSD and OpenBSD use 18 as DLT_PFSYNC.  This may introduce compat
issue with dump files generated using DLT_PFSYNC before this change.