- Add support for attaching alternative DLTs to an interface.

- Add support for attaching alternative DLTs to an interface.
  The function is named bpfattach_dlt, FreeBSD used bpfattach2.
- Change bpf_mtap to take the bpf_if directly.
- Add support for BIOCSDLT and BIOCGDLT to recieve a list of DLTs
  available on an interface.

Obtained-from: FreeBSD

- Add bpf_ptap, which takes an mbuf and a header, builds a temporary
  mbuf chain and calls bpf_mtap on that.

Inspired-by: FreeBSD's bpf_mtap2
- Use the new interface for all drivers doing this by hand before.
- Include the formerly commented out support for radio headers in wi(4)
  and wlan(4).
- Change if_loop, i4b_ipr, disc and ic to prepend a uint32_t, not an int.