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>