Radar FFT and PHY errors

Some later-model 802.11n hardware (AR9130 and later) is capable of reporting FFT data along side normal radar PHY errors.

• http://people.freebsd.org/~adrian/ath/2012-06-19-ath-radiotap.diff

This code includes a library to parse basic radar frames as well as the radiotap / bpf code needed to dump out the PHY error frames. It requires the above patch to be applied and 'dev.ath.X.monpass' to be set appropriately (see below.)

• http://svn.freebsd.org/base/user/adrian/ath_radar_stuff/

(TBD)

• apply the patch
• if you want to enable radar phy errors on all channels, just modify sys/dev/ath/ath_dfs/null/dfs_null.c and modify ath_dfs_radar_enable() to always enable the radar bits (comment out the DFS check).
• Allow PHY errors to be spat out via radiotap: sysctl dev.ath.X.monpass=0x02
• start a radiotap session on the relevant wlan interface.