o record tsf in tx+rx frames
o switch from raw rssi to dbm for signal data and record both
signal and noise floor data (hacked for now to assume a fixed
noise floor; is correct with new hal)
o add monpass sysctl to control which rx'd frames are passed
up with errors; especially useful to see frames with CRC errors
o mark 'd packets w/ a CRC error with radiotap's BADFCS flag
Also add placeholder code for calibrating the noise floor when
using newer hals.
Reviewed by: avatar
MFC after: 1 week
7b0c77eca9