Add a new option, WITH_RADIOTAP. Import David Young's patches for using the
new net80211 radiotap interface. This can be activated once the tcpdump port
is built and installed using the datalink type IEEE802_11_RADIO. Tested with
a wi(4), OEM PRISM2, 1.4.9 STA firmware.
Submitted by: David Young
Sponsored by: consume.net