net: sch: simplify condtion for selecting mini_Qdisc_pair buffer

The only valid values for a miniq pointer are NULL or a pointer to
miniq1 or miniq2, so testing for miniq_old != &miniq1 is functionally
equivalent to testing that it is NULL or equal to &miniq2.

Suggested-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Seth Forshee <sforshee@digitalocean.com>
Link: https://lore.kernel.org/r/20211026183721.137930-1-seth@forshee.me
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/sched/sch_generic.c

@@ -1500,7 +1500,7 @@ void mini_qdisc_pair_swap(struct mini_Qdisc_pair *miniqp,
 	if (!tp_head) {
 		RCU_INIT_POINTER(*miniqp->p_miniq, NULL);
 	} else {
-		miniq = !miniq_old || miniq_old == &miniqp->miniq2 ?
+		miniq = miniq_old != &miniqp->miniq1 ?
 			&miniqp->miniq1 : &miniqp->miniq2;
 
 		/* We need to make sure that readers won't see the miniq