cfg80211: document sched_scan_stop synchronous behaviour

Due to userspace assumptions, the sched_scan_stop operation must
be synchronous, i.e. once it returns a new scheduled scan must be
able to start immediately. Document this in the API.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>

diff --cc include/net/cfg80211.h
Simple merge

diff --cc include/uapi/linux/nl80211.h
Simple merge