Move code from ipw2100_wpa_enable to IPW2100_PARAM_DROP_UNENCRYPTED to

support wpa_supplicant with open AP. We need this to make driver_ipw
work.

driver_ext has already had the similar code with the WE-18 support
added.

Signed-off-by: James Ketrenos <jketreno@linux.intel.com>