Add support for RVI (Remote Virtual Interface) interfaces

[choll]

This seems to give ethernet frames, but instead of the link type being DLT_EN10MB it is 149. bpf.h has:

#define DLT_USER2       149
#define DLT_PKTAP       DLT_USER2

There is also IFT_PKTAP, but sysctl seems to return IFT_OTHER ?

[choll]

DLT_PKTAP is defined by pcap/bpf.h, not net/bpf

[choll]

It doesn't produce ethernet frames. tcpdump saves rvi captures as ethernet though.

[choll]

http://www.opensource.apple.com/source/xnu/xnu-2422.1.72/bsd/net/pktap.h

The header is struct pktap_header. The pth_dlt field is DLT_EN10MB, after that it seems to be an ethernet frame.

[choll]

fix issue #45, rvi support

→ <<cset 583920c507a2>>