[PATCH] softmac: handle iw_mode properly

Below patch allows using iw_mode auto with softmac. bcm43xx forces managed
so this bug wasn't noticed earlier, but this was one of the problems why
zd1211 didn't work earlier.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>