WPS: Change wpa_supplicant wps_reg to not send out M8

WPS: Change wpa_supplicant wps_reg to not send out M8

Since we do not currently support changing the AP settings received
from M7, there is no point in actually sending out the M8 that would
likely trigger the AP to reconfigure itself and potentially reboot.
For now, we just receive the AP settings in M7 and add a local network
configuration block based on those, but NACK the message. This makes
wps_reg work like wps_pin, but by using the AP PIN instead of a client
PIN.