Prints out generated asm for a pcap expression.

Example of use:

$ ./pf_pcap_asm
$ ./pf_pcap_asm "<pcap-expression>" (default "tcp port 80")

NOTE: The file used for packet filtering is a 1GB file from pflua-bench, so
it's necessary to clone that repo, uncompress the file and create a symbolic
link to it. See instructions in src/pf_pcap_asm.lua.