ath9k ath_ani_calibrate

I was seeing this function showing up consistently while running powertop. It 
seems that ANI is always enabled by default, and I didn't see any ioctl or 
config option to disable it. It sets a timer to wakeup every 100ms and do 
whatever calibration it's trying to do. I changed the ANI_POLLINTERVAL to 
1000ms and recompiled, and haven't noticed any ill effect yet. Is there any 
reason why this calibration needs to happen 10 times a second? Will it still 
be useful if it were toned down, to 250ms, or 500ms? (Note - because the 
driver takes the minimum of the active calibration intervals, and 
ANI_POLLINTERVAL is the smallest, it is always the one that wins...)

With this changed to 1sec, I still see the ath9k driver waking up 10-12 
times/second but I presume that's in response to random packets from the AP.
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