iwmc3200wifi: Try shared auth when open WEP fails

When we fail to associate with an open WEP AP, we fall back to shared auth.
This allows us to support joining a shared auth WEP AP with iwconfig.

Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>