#580: pf_ring support

The PF_RING user land library seems to be LGPL; the code itself seems to disagree with itself as to which version applies (pfring.h says 2 or later, pfring.c says 3 or later). COPYING is LGPL v3, so I'd assume that was the intended license.


Ugh. Oh well, at least we will only need to link with it.


(Please make sure to add such things to the tracker ticket, that's
very valuable information. If your email address matches your tracker
account, you should be able to email it there directly).