mac80211: fix LED in idle handling

feng xiangjun reports that my

commit 382a103b2b528a3085cde4ac56fc69d92a828b72
Author: Johannes Berg <johannes.berg@intel.com>
Date:   Fri Mar 22 22:30:09 2013 +0100

    mac80211: fix idle handling sequence

broke the wireless status LED. The reason is that
we now call ieee80211_idle_off() when the channel
context is assigned, and that doesn't recalculate
the LED state. Fix this by making that function a
wrapper around most of idle recalculation while
forcing active.

Reported-by: feng xiangjun <fengxj325@gmail.com>
Tested-by: feng xiangjun <fengxj325@gmail.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>