luci-mod-network: wireless.js: add wifi-iface macaddr random support

Add ability to choose random or custom mac address for wifi-iface.
By default the driver mac address is used and this special feature needs
to be supported by the wireless driver.

Signed-off-by: Manas Sambhus <manas.sambhus+github@gmail.com>
[ drop redundant tags and improve commit description ]
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>