mac80211: fix txq queue related crashes

mac80211: fix txq queue related crashes

commit 2a58d42c1e018ad514d4e23fd33fb2ded95d3ee6 upstream.

The driver can access the queue simultanously
while mac80211 tears down the interface. Without
spinlock protection this could lead to corrupting
sk_buff_head and subsequently to an invalid
pointer dereference.

Fixes: ba8c3d6f16a1 ("mac80211: add an intermediate software queue implementation")
Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>