rndis_wlan: do not try to restore wpa keys using add_wep_key()

set_infra_mode() tried to restore wpa keys using add_wep_key(). This never
worked so prevent driver from trying.

Signed-off-by: Jussi Kivilinna <jussi.kivilinna@mbnet.fi>
Signed-off-by: John W. Linville <linville@tuxdriver.com>