orinoco: allow IW_AUTH_MFP to pass through

The card doesn't support MFP, so silently accept DISABLED and OPTIONAL
settings.

This avoids the following failure in wpa_supplicant logs:

State: SCANNING -> ASSOCIATING
wpa_driver_wext_set_operstate: operstate 0->0 (DORMANT)
netlink: Operstate: linkmode=-1, operstate=5
wpa_driver_wext_associate
wpa_driver_wext_set_drop_unencrypted
wpa_driver_wext_set_psk
wpa_driver_wext_associate: assoc failed because set_auth_param(IW_AUTH_MFP) failed
Association request to the driver failed

Signed-off by: David Kilroy <kilroyd@googlemail.com>
Reported by: Giacomo Comes <comes@naic.edu>

Signed-off-by: John W. Linville <linville@tuxdriver.com>