nl80211: support 4-way handshake offloading for WPA/WPA2-PSK in AP mode

nl80211: support 4-way handshake offloading for WPA/WPA2-PSK in AP mode

Let drivers advertise support for AP-mode WPA/WPA2-PSK 4-way handshake
offloading with a new NL80211_EXT_FEATURE_4WAY_HANDSHAKE_AP_PSK flag.

Extend use of NL80211_ATTR_PMK attribute indicating it might be passed
as part of NL80211_CMD_START_AP command, and contain the PSK (which is
the PMK, hence the name).

The driver is assumed to handle the 4-way handshake by itself in this
case, instead of relying on userspace.

Signed-off-by: Chung-Hsien Hsu <stanley.hsu@cypress.com>
Signed-off-by: Chi-Hsien Lin <chi-hsien.lin@cypress.com>
Link: https://lore.kernel.org/r/20200623134938.39997-2-chi-hsien.lin@cypress.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>