[PATCH] mac80211: don't allow scanning in monitor mode

zd1211rw gets confused when the user asks for a scan when the device is
in monitor mode. This patch tightens up the SIWSCAN handler to deny the scan
under these conditions.

Signed-off-by: Daniel Drake <dsd@gentoo.org>
Signed-off-by: Jiri Benc <jbenc@suse.cz>
Signed-off-by: John W. Linville <linville@tuxdriver.com>