Add libpcap / winpcap to image

[andrewkroh]

Packetbeat builds libpcap from source every time packaging runs. It downloads 1.8.1 and builds a static library. It would be beneficial to do this once when the images are built rather then anytime packetbeat is built. This is where Packetbeat run the build commands:

https://github.com/elastic/beats/blob/941709b4b9455a435b4afba9b2704360be7e75bd/packetbeat/magefile.go#L254-L285

And on Windows it installs WinPCAP so that it can link against it (dynamically). So these commands could also be added to the image.

https://github.com/elastic/beats/blob/941709b4b9455a435b4afba9b2704360be7e75bd/packetbeat/magefile.go#L377-L409

[kuisathaverat]

for Linux it is possible and easy, for windows the wpcap.def depends on the beats, I am not sure is not possible to generate a def file for all the beats.

[andrewkroh]

I think it only depends on beats in that elastic/beats has a copy of the DLL needed to create the winpcap static library. elastic/beats#1259 (comment)