Fix bugs around wrong argument to gettimeofday, pcap_offline_filter

* src/pf.lua: Create a pcap_pkthdr instead of a pcap_record.  They're
  different on 64-bit systems...

* src/pf/libpcap.lua: Update pcap_offline_filter prototype and selftest
  message.

* src/pf/savefile.lua: Remove struct pcap_record_extra, as it's not
  used.

* src/pf/types.lua: Add pcap_pkthdr.

* src/pf/utils.lua: Fix suseconds_t type (!).