Staging: wlan-ng: replace switch-case statements with macro

This patch removes multiple switch-case statements
with a new macro. The macro will generate the
corresponding bit mask based on the key index
received as input.

Chances since v1:
Corrected patch title

Signed-off-by: Claudiu Beznea <claudiu.beznea@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>