net_sched: make cls_ops->change and cls_ops->delete optional

Some schedulers don't support creating, changing or deleting classes.
Make the respective callbacks optionally and consistently return
-EOPNOTSUPP for unsupported operations, instead of currently either
-EOPNOTSUPP, -ENOSYS or no error.

In case of sch_prio and sch_multiq, the removed operations additionally
checked for an invalid class. This is not necessary since the class
argument can only orginate from ->get() or in case of ->change is 0
for creation of new classes, in which case ->change() incorrectly
returned -ENOENT.

As a side-effect, this patch fixes a possible (root-only) NULL pointer
function call in sch_ingress, which didn't implement a so far mandatory
->delete() operation.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_red.c

@@ -308,17 +308,6 @@ static void red_put(struct Qdisc *sch, unsigned long arg)
 	return;
 }
 
-static int red_change_class(struct Qdisc *sch, u32 classid, u32 parentid,
-			    struct nlattr **tca, unsigned long *arg)
-{
-	return -ENOSYS;
-}
-
-static int red_delete(struct Qdisc *sch, unsigned long cl)
-{
-	return -ENOSYS;
-}
-
 static void red_walk(struct Qdisc *sch, struct qdisc_walker *walker)
 {
 	if (!walker->stop) {
@@ -336,8 +325,6 @@ static const struct Qdisc_class_ops red_class_ops = {
 	.leaf		=	red_leaf,
 	.get		=	red_get,
 	.put		=	red_put,
-	.change		=	red_change_class,
-	.delete		=	red_delete,
 	.walk		=	red_walk,
 	.dump		=	red_dump_class,
 };