mac80211: fill rate filter for internal scan requests

The rates bitmap for internal scan requests shoud be filled,
otherwise there will be probe requests with zero rates supported.

Signed-off-by: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
Signed-off-by: Mathias Kretschmer <mathias.kretschmer@fokus.fraunhofer.de>
Cc: stable@vger.kernel.org
Signed-off-by: John W. Linville <linville@tuxdriver.com>