wifi: mac80211: clear frame buffer to never leak stack

In disconnect paths paths, local frame buffers are used
to build deauthentication frames to send them over the
air and as notifications to userspace. Some internal
error paths (that, given no other bugs, cannot happen)
don't always initialize the buffers before sending them
to userspace, so in the presence of other bugs they can
leak stack content. Initialize the buffers to avoid the
possibility of this happening.

Suggested-by: Zhongqiu Han <quic_zhonhan@quicinc.com>
Link: https://patch.msgid.link/20250701072213.13004-2-johannes@sipsolutions.net


Signed-off-by: Johannes Berg <johannes.berg@intel.com>