mac80211: Fix probe request filtering in IBSS mode

We only reply to probe request if either the requested SSID is the
broadcast SSID or if the requested SSID matches our own SSID. This
latter case was not properly handled since we were replying to different
SSID with the same length as our own SSID.

Signed-off-by: Benoit Papillault <benoit.papillault@free.fr>
Cc: stable@kernel.org
Signed-off-by: John W. Linville <linville@tuxdriver.com>