mac80211: make sure TDLS teardown packet is sent on time

Since the teardown packet is created while the queues are
stopped, it isn't sent immediately, but rather is pending.
To be sure that when we flush the queues prior to destroying
the station we also send this packet - the tasklet handling
pending packets is invoked to flush the packets.

Signed-off-by: Liad Kaufman <liad.kaufman@intel.com>
Reviewed-by: ArikX Nemtsov <arik@wizery.com>
Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>