iwlwifi: change default led mode for different devices

Set the default led mode for different devices.

For the newer devices such as 6000g2a, 6000g2b and newer,
the default led mode is On/Off instead of blinking.

The led_mode still can be control through module parameter
  0: system default
  1: On/Off
  2: blinking

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>