cfg80211: remove spurious __KERNEL__ ifdef

The net/cfg80211.h header file isn't exported to
userspace, so there's no need for any kind of
__KERNEL__ protection in it. If it was exported,
everything else in it would need protection as
well, not just the logging stuff ...

Cc:Joe Perches <joe@perches.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>