qcacld-2.0 to qcacld-3.0 propagation
In some case, scan_block_work will be scheduled, but NETDEV_DOWN will
come before scan_block_work executed, it will lead to crash. Because
in this case it will call ___cfg80211_scan_done to free scan request in
cfg80211_netdev_notifier_call firstly, but it will access scan request
in wlan_hdd_cfg80211_scan_block_cb afterwards, so it will crash.
Add flush scan_block_work process when receive NETDEV_GOING_DOWN notifier.
Change-Id: Iada4b907f5fb03871406904340e21b6cdf89306f
CRs-Fixed: 2034794
eaa33eee78