nl80211: fix sched scan netlink socket owner destruction

A single netlink socket might own multiple interfaces *and* a
scheduled scan request (which might belong to another interface),
so when it goes away both may need to be destroyed.

Remove the schedule_scan_stop indirection to fix this - it's only
needed for interface destruction because of the way this works
right now, with a single work taking care of all interfaces.

Cc: stable@vger.kernel.org
Fixes: 93a1e86c

 ("nl80211: Stop scheduled scan if netlink client disappears")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>