Fix and update Npcap example code

The code examples we provide with Npcap (which we inherited from the now-obsolete WinPcap) need to be updated for several reasons:

• Doesn't always handle the new VLAN tags feature properly. For example it treats ethernet headers as always 14 bytes in various places like "ih = (ip_header *) (pkt_data + 14); //length of ethernet header"
• The fact that we have 2 separate trees: one is supposed to be mingw-compatible, I think, but we haven't really tried that.
• Most uses older libpcap API functions like pcap_open_live instead of pcap_create/pcap_activate.
• There are likely bugs in general that we've never checked for.
• very ugly code with mixed tabs/spaces
• Only enable promiscuous mode in the examples in cases where it is likely to be particularly useful rather than as a general approach. Most users don't need it and it harms performance when they set it (sometimes by copying our samples) in cases where it isn't needed. The switch to the pcap_create/pcap_activate API may resolve this since it doesn't have the promisc boolean like pcap_open_live does.

Some users may (reasonably) start from our sample code, so it is especially important for us to set a good example.

Locate the two example trees and audit the packet-header handling, pcap_open_live uses, VLAN assumptions, promiscuous-mode settings, and formatting. Compare the examples with the current libpcap API and verify the result across the stated compatibility targets; done means the examples are reviewed and updated consistently, with their existing bugs and assumptions checked.