staging: wilc1000: set bssid with mode

This patch add new argument mode to wilc_wlan_set_bssid and define mode in
struct wilc_vif also. The mode is used by get_if_handler function to get proper
netdevice for each mode.
The get_if_handler is changed together. Remove invalid handle codes and
add mode condition to get netdevice for the mode.

Signed-off-by: Glen Lee <glen.lee@atmel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>