luci-app-travelmate: fix QR-Code generation

* fixed #6377
   According to https://www.wi-fi.org/download.php?file=/sites/default/files/private/WPA3_Specification_v3.0.pdf (chapter 7)
   set the security type to 'WPA'. Tested with an Android device (Samsung 10e) and various WPA2- and WPA3-AP modes
   (incl. OWE, but without enterprise variants).

Signed-off-by: Dirk Brenken <dev@brenken.org>