cfg80211: Add support for userspace to reset stations in IBSS mode

Sometimes, userspace is able to detect that a peer silently lost its
state (like, if the peer reboots). wpa_supplicant does this for IBSS-RSN
by registering for auth/deauth frames, but when it detects this, it is
only able to remove the encryption keys of the peer and close its port.

However, the kernel also hold other state about the station, such as BA
sessions, probe response parameters and the like.  They also need to be
resetted correctly.

This patch adds the NL80211_EXT_FEATURE_DEL_IBSS_STA feature flag
indicating the driver accepts deleting stations in IBSS mode, which
should send a deauth and reset the state of the station, just like in
mesh point mode.
Signed-off-by: Nicolas Cavallari <nicolas.cavallari@green-communications.fr>
Link: https://lore.kernel.org/r/20200305135754.12094-1-cavallar@lri.fr
[preserve -EINVAL return]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

include/uapi/linux/nl80211.h

@@ -5654,6 +5654,9 @@ enum nl80211_feature_flags {
  *
  * @NL80211_EXT_FEATURE_PROTECTED_TWT: Driver supports protected TWT frames
  *
+ * @NL80211_EXT_FEATURE_DEL_IBSS_STA: The driver supports removing stations
+ *      in IBSS mode, essentially by dropping their state.
+ *
  * @NUM_NL80211_EXT_FEATURES: number of extended features.
  * @MAX_NL80211_EXT_FEATURES: highest extended feature index.
  */
@@ -5704,6 +5707,7 @@ enum nl80211_ext_feature_index {
 	NL80211_EXT_FEATURE_BEACON_PROTECTION,
 	NL80211_EXT_FEATURE_CONTROL_PORT_NO_PREAUTH,
 	NL80211_EXT_FEATURE_PROTECTED_TWT,
+	NL80211_EXT_FEATURE_DEL_IBSS_STA,
 
 	/* add new features before the definition below */
 	NUM_NL80211_EXT_FEATURES,

net/wireless/nl80211.c

@@ -6286,7 +6286,12 @@ static int nl80211_del_station(struct sk_buff *skb, struct genl_info *info)
 	if (dev->ieee80211_ptr->iftype != NL80211_IFTYPE_AP &&
 	    dev->ieee80211_ptr->iftype != NL80211_IFTYPE_AP_VLAN &&
 	    dev->ieee80211_ptr->iftype != NL80211_IFTYPE_MESH_POINT &&
-	    dev->ieee80211_ptr->iftype != NL80211_IFTYPE_P2P_GO)
+	    dev->ieee80211_ptr->iftype != NL80211_IFTYPE_P2P_GO &&
+	    dev->ieee80211_ptr->iftype != NL80211_IFTYPE_ADHOC)
+		return -EINVAL;
+	if (dev->ieee80211_ptr->iftype == NL80211_IFTYPE_ADHOC &&
+	    !wiphy_ext_feature_isset(&rdev->wiphy,
+				     NL80211_EXT_FEATURE_DEL_IBSS_STA))
 		return -EINVAL;
 
 	if (!rdev->ops->del_station)