rndis_wlan: handle NL80211_AUTHTYPE_AUTOMATIC

rndis_wlan didn't know about NL80211_AUTHTYPE_AUTOMATIC and simple
setup with 'iwconfig wlan essid no-encrypt' would fail (ENOSUPP).

v2: use NDIS_80211_AUTH_AUTO_SWITCH instead of _OPEN.
    This will make device try shared key auth first, then open.

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