b43: Fix beacon problem in ad-hoc mode

In ad-hoc mode, driver b43 does not issue beacons.

Signed-off-by: Manual Munz <freifunk@somakoma.de>
Tested-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Cc: Stable <stable@kernel.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>