Fix QMI USSD async response handling and prevent st terminal popup

overlay/rootfs/usr/bin/sxmo_modemmonitor.sh

@@ -115,8 +115,8 @@ mainloop() {
       esac
 
       if [ "$CHANGED" = "1" ]; then
-        # Fetch message (third argument) in sxmo_ussd.sh to save time in this loop
-        sxmo_terminal.sh sxmo_ussd.sh "$MODEM" "$TYPE" "" &
+        # Handle unsolicited USSD in background without spawning a terminal window
+        sxmo_ussd.sh "$MODEM" "$TYPE" "" &
       fi
 
     done &