BACKPORT: nl80211: Stop scheduled scan if netlink client disappears

(cherry pick from commit 93a1e86c)

An attribute NL80211_ATTR_SOCKET_OWNER can be set by the scan initiator.
If present, the attribute will cause the scan to be stopped if the client
dies.

Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Bug: 25561044
Change-Id: I2343e494d2f4b4154ce945b61b97a68384fa92c1