[PATCH] bcm43xx: improved statistics

This patch improves the statistics returned from
bcm43xx_get_wireless_stats. The signal level comes from smoothing the
"rssi" value returned by the firmware after it is converted into a
dBm value by the driver. The quality value is a hack derived from the
smoothed level and an assumed RX_POWER_MAX of -10 dBM. The noise value
is still the one calculated from the clean-room formula. On my system,
this is roughly -65 dBm, which seems too high.

The revised version uses the ieee80211 spinlock to protect traversing
of the network list.

Signed-Off-By: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>