mac80211: prevent tuning during scanning

Postpone calling ieee80211_hw_config if hardware scanning is active.
This is similar to solution for software scanning where channel setting
is delayed until scan complete.

Signed-off-by: Mohamed Abbas <mohamed.abbas@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Acked-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>