Extend WFP callout to be able to capture other traffic types

Windows offers 2 different ways for drivers to inspect network traffic: NDIS LWF and WFP. Npcap uses NDIS LWF to see traffic on the stack between protocol drivers and miniport drivers. Some unusual network situations like VPNs may use a different data path that doesn't pass through our driver. WFP exists in a different part of the stack entirely, and could allow us to inspect traffic at different places, including prior to IPSEC VPN encapsulation. Because the semantics of traffic are different for WFP, we'd have to define and implement an extension to our existing API to let programs use it. The major difference is that there wouldn't be a concept of "capture traffic on this adapter" but rather "capture traffic at this point in the stack" which is pre-routing. That could be analogous to the "any" pseudo-device from libpcap on Linux.

Related: #257

Start by reviewing the existing capture API and the related discussion in #257, then compare the NDIS LWF path with the proposed WFP path. The work is done when the API extension is defined and implemented for pre-routing WFP capture, including traffic types beyond adapter-based capture.