mac80211: remove WARN_ON() from ieee80211_hw_config

ieee80211_hw_config can return an error when the hardware
has rfkill enabled. A WARN_ON() is too harsh for this
failure as it is a valid scenario. Only comment this warning
as we would like to have it back when rfkill is integrated into
mac80211.

Also reintroduce propagation of error if ieee80211_hw_config fails
in ieee80211_config_beacon.

This patch partially reverts patch:
5f0387fc3337ca26f0745f945f550f0c3734960f
"mac80211: clean up ieee80211_hw_config errors"

Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>