cfg80211: Specify frame and reason code for NL80211_CMD_DEL_STATION

The optional NL80211_ATTR_MGMT_SUBTYPE and NL80211_ATTR_REASON_CODE
attributes can now be included in NL80211_CMD_DEL_STATION to indicate to
the driver which frame (Deauthentication/Disassociation) and reason code
in that frame should be used to indicate removal to the specific
station. This is used by drivers that implement AP SME and generate
those frames internally.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>