airo: fix test for FLAG_RADIO_DOWN

We should be doing a shift (1 << FLAG_RADIO_DOWN) here before testing
the flag.  As luck would have it, this test works almost correctly.
The current code tests for FLAG_RADIO_OFF instead of FLAG_RADIO_DOWN.

#define FLAG_RADIO_OFF  0       /* User disabling of MAC */
#define FLAG_RADIO_DOWN 1       /* ifup/ifdown disabling of MAC */

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>