to do about the few cases where the HAL state isn't available (regdomain)
or isn't yet setup (probe/attach.)
The global ath_hal_debug now affects all instances of the HAL.
This also restores the ability for probe/attach debugging to work; as
the sysctl tree may not be attached at that point. Users can just set
the global "hw.ath.hal.debug" to a suitable value to enable probe/attach
related debugging.
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