WPS: Added callback for failure-after-M2/M2D

This callback is now used to stop wpa_supplicant from trying to continue
using parameters (most likely, device password) that do not work in a
loop. In addition, wpa_gui can now notify user of failed registration.

wpa_supplicant/wpa_gui-qt4/wpagui.cpp

@@ -804,6 +804,8 @@ void WpaGui::processMsg(char *msg)
 			wpsStatusText->setText("Registration started");
 	} else if (str_match(pos, WPS_EVENT_M2D)) {
 		wpsStatusText->setText("Registrar does not yet know PIN");
+	} else if (str_match(pos, WPS_EVENT_FAIL)) {
+		wpsStatusText->setText("Registration failed");
 	}
 }