cls_flower: Fix missing free of rhashtable

When destroying the instance, destroy the head rhashtable.

Fixes: 05cd271fd61a ("cls_flower: Support multiple masks per priority")
Reported-by: Vlad Buslov <vladbu@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Paul Blakey <paulb@mellanox.com>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/cls_flower.c

@@ -326,6 +326,8 @@ static void fl_destroy_sleepable(struct work_struct *work)
 	struct cls_fl_head *head = container_of(to_rcu_work(work),
 						struct cls_fl_head,
 						rwork);
+
+	rhashtable_destroy(&head->ht);
 	kfree(head);
 	module_put(THIS_MODULE);
 }