pflogd: Define structures removed in libpcap-1.10.5

[jrm]

Summary

In libpcap-1.10.5, two structures that we rely on, pcap_timeval and
pcap_sf_pkthdr, were made private.

https://github.com/the-tcpdump-group/libpcap/commit/c2d8cbb977963be1f6cb07863e5bb59609e87fae

Temporarily define them here to fix the build. kp and I will
investigate a permanent solution at EuroBSDCon in Dublin.

[jrm]

Remove unintended changes

[jrm]

Fix commit log header