This provides some of the same info found in
the ath9k_htc debugfs through the standard ethtool stats API.

This logic is only supported when ath9k_htc debugfs kernel
feature is enabled, since that is the only time stats
are actually gathered.
Signed-off-by: NBen Greear <greearb@candelatech.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>