sched/numa: Fix NUMA_DIRECT topology identification

Systems which have all nodes at a distance of at most 1 hop should be
identified as 'NUMA_DIRECT'.

However, the scheduler incorrectly identifies it as 'NUMA_BACKPLANE'.
This is because 'n' is assigned to sched_max_numa_distance but the
code (mis)interprets it to mean 'number of hops'.

Rik had actually used sched_domains_numa_levels for detecting a
'NUMA_DIRECT' topology:

  http://marc.info/?l=linux-kernel&m=141279712429834&w=2

But that was changed when he removed the hops table in the
subsequent version:

  http://marc.info/?l=linux-kernel&m=141353106106771&w=2

Fixing the issue here.
Signed-off-by: NAravind Gopalakrishnan <Aravind.Gopalakrishnan@amd.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: NRik van Riel <riel@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1439256048-3748-1-git-send-email-Aravind.Gopalakrishnan@amd.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

kernel/sched/core.c

@@ -6444,8 +6444,10 @@ static void init_numa_topology_type(void)
 
 	n = sched_max_numa_distance;
 
-	if (n <= 1)
+	if (sched_domains_numa_levels <= 1) {
 		sched_numa_topology_type = NUMA_DIRECT;
+		return;
+	}
 
 	for_each_online_node(a) {
 		for_each_online_node(b) {