mac80211: Fix kernel panic due to use of txq after free

The txq of vif is added to active_txqs list for ATF TXQ scheduling
in the function ieee80211_queue_skb(), but it was not properly removed
before freeing the txq object. It was causing use after free of the txq
objects from the active_txqs list, result was kernel panic
due to invalid memory access.

Fix kernel invalid memory access by properly removing txq object
from active_txqs list before free the object.

Signed-off-by: Bhagavathi Perumal S <bperumal@codeaurora.org>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>