mac80211 scan processing could get stuck if roc work for pending, but
not started when a scan request was deferred due to such roc item.
Normally the deferred scan would be started from
ieee80211_start_next_roc(), but ieee80211_sw_roc_work() calls that only
if the finished ROC was started. Fix this by calling
ieee80211_run_deferred_scan() in the case the last ROC was not actually
started.

This issue was hit relatively easily in P2P find operations where Listen
state (remain-on-channel) and Search state (scan) are repeated in a
loop.
Signed-off-by: Jouni Malinen <j@w1.fi>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>