[NET_SCHED]: turn PSCHED_TDIFF_SAFE into inline function

Also rename to psched_tdiff_bounded.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/sched/sch_htb.c b/net/sched/sch_htb.c
index b7abd0a..71e4c92 100644
--- a/net/sched/sch_htb.c
+++ b/net/sched/sch_htb.c
@@ -729,7 +729,7 @@
 	cl->T = toks
 
 	while (cl) {
-		diff = PSCHED_TDIFF_SAFE(q->now, cl->t_c, (u32) cl->mbuffer);
+		diff = psched_tdiff_bounded(q->now, cl->t_c, cl->mbuffer);
 		if (cl->level >= level) {
 			if (cl->level == level)
 				cl->xstats.lends++;
@@ -789,7 +789,7 @@
 			return cl->pq_key;
 
 		htb_safe_rb_erase(p, q->wait_pq + level);
-		diff = PSCHED_TDIFF_SAFE(q->now, cl->t_c, (u32) cl->mbuffer);
+		diff = psched_tdiff_bounded(q->now, cl->t_c, cl->mbuffer);
 		htb_change_class_mode(q, cl, &diff);
 		if (cl->cmode != HTB_CAN_SEND)
 			htb_add_to_wait_tree(q, cl, diff);