hwdb: Use wlan keycode for all Dell systems (#8762)

Once the seat is acquired, gnome-settings-daemon (GSD) takes full
control of rfkill by sending RFKILL_IOCTL_NOINPUT ioctl to disable
rfkill control in kernel.

Since GSD expects wlan keycode when the hotkey gets pressed, we should
change the "unknown" to "wlan" accordingly.

Tested under both GNOME and KDE.