Add support for Apple specific process information blocks

[jgamba-te]

Hello,

this PR adds support for Apple specific PIB (process information blocks) which contain metadata about the process originating a given packet. These blocks contain some basic info about the processes (process name and command for instance). There is no public documentation about these blocks that I could find but Apple did release their version of libpcap which contains some details (see for instance: https://github.com/apple-opensource/libpcap/blob/master/libpcap/pcap/pcap-ng.h#L330).

To test this you will need a Mac and capture packets with the PKTAP interface:

sudo tcpdump -i eno1,pktap -w capture.pcap

[chifflier]

Hi,
Thank you for your contribution.
This looks good to me, even if there are no specifications nor test files that I can use.
Merged, thanks