ap_setup_locked=2 can now be used to enable a special mode where
WPS ER can learn the current AP settings, but cannot change then.
In other words, the protocol is allowed to continue past M2, but
is stopped at M7 when AP is in this mode. WPS IE does not
advertise AP Setup Locked in this case to avoid interoperability
issues.
In wpa_supplicant, use ap_setup_locked=2 by default. Since the AP PIN
is disabled by default, this does not enable any new functionality
automatically. To allow the read-only ER to go through the protocol,
wps_ap_pin command needs to be used to enable the AP PIN.
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