VLAN tag reporting

[ransford]

Is your feature request related to a problem? Please describe.
Without VLAN tag information, it can be harder to track down a specific device.

Describe the solution you'd like
Include VLAN information from gopacket's CaptureInfo struct. https://godoc.org/github.com/google/gopacket#CaptureInfo.

[ransford]

Note that the availability of VLAN tags depends on the source of the packets; afpacket on Linux looks promising, but others (macOS, Windows) may not be as rich. Probably log some debug-level information about the packet source at startup.