ath9k: fix listening to idle requests

The way idle configuration detection was implemented as
busted due to the fact that it assumed the ath9k virtual wiphy,
the aphy, would be marked as inactive if it was not used but
it turns out an aphy is always active if its the only wiphy
present. We need to distinguish between aphy activity and
idleness so we now add an idle bool for the aphy and mark
it as such based on the passed IEEE80211_CONF_CHANGE_IDLE
from mac80211.

Previous to all_wiphys_idle would never be true when using
only one device so we never really were using
IEEE80211_CONF_CHANGE_IDLE -- we never turned the radio
off or on upon IEEE80211_CONF_CHANGE_IDLE changes as radio
changes depended on all_wiphys_idle being true either to
turn the radio on or off. Since it was always false for
one device this code was doing nothing.

Cc: Jouni.Malinen <Jouni.Malinen@atheros.com>
Reported-by: Vasanthakumar Thiagarajan <vasanth@atheros.com>
Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>