WPS: Convert WPA/TKIP-only to WPA+WPA2 mixed mode credential
This case of accepting WPA/TKIP-only credential based on internal
registrar request to configure an AP to use TKIP was still remaining
while all the WPS cases were supposed to enable mixed mode
automatically. This is bit of a corner case since this is based on
explicit local request to configure TKIP, but anyway, convert this one
as well to allow WPA2/CCMP to be used.