cfg80211: add missing policy for NL80211_ATTR_STATUS_CODE

The nl80211_policy is missing for NL80211_ATTR_STATUS_CODE attribute.
As a result, for strictly validated commands, it's assumed to not be
supported.

Signed-off-by: Sergey Matyukevich <sergey.matyukevich.os@quantenna.com>
Link: https://lore.kernel.org/r/20200213131608.10541-2-sergey.matyukevich.os@quantenna.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
