WPS: SelectedRegistrar expiration for internal PIN registrar

WPS: SelectedRegistrar expiration for internal PIN registrar

Though we have such a timeout when handling SetSelectedRegistrar UPnP
message from an external registrar, it looks like we don't have one when
the internal registrar is activated for PIN connection. Thus we set the
SelectedRegistrar flag when AP is activated for PIN connection but we
never reset it - not by some timeout, nor when registration succeeds.
This lead to situations where AP everlastingly declare that it is
activated for WPS PIN connection when in reality it is not.

Use the same timeout (and also success with PIN) to clear the selected
registrar flag when using internal registrar, too.