rndis_wlan: fix broken logic in add_wep_key()

add_wep_key() tries to check if key length is not 5 AND not 13
but uses (key_len != 5 || key_len != 13) instead. Fix this.

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