BUG/MINOR: threads: fix the process range of thread masks

Commit 421f02e ("MINOR: threads: add a MAX_THREADS define instead of
LONGBITS") used a MAX_THREADS macros to fix threads limits. However,
one change was wrong as it affected the upper bound of the process
loop when setting threads masks. No backport is needed.
diff --git a/src/listener.c b/src/listener.c
index 553607a..40419d5 100644
--- a/src/listener.c
+++ b/src/listener.c
@@ -979,7 +979,7 @@
 
 	conf->bind_proc |= proc;
 	if (thread) {
-		for (i = 0; i < MAX_THREADS; i++)
+		for (i = 0; i < LONGBITS; i++)
 			if (!proc || (proc & (1UL << i)))
 				conf->bind_thread[i] |= thread;
 	}