MINOR: thread: get rid of MAX_THREADS_MASK

This macro was used both for binding and for lookups. When binding tasks
or FDs, using all_threads_mask instead is better as it will later be per
group. For lookups, ~0UL always does the job. Thus in practice the macro
was already almost not used anymore since the rest of the code could run
fine with a constant of all ones there.
diff --git a/src/check.c b/src/check.c
index f789959..ada79ed 100644
--- a/src/check.c
+++ b/src/check.c
@@ -1217,7 +1217,7 @@
         if (LIST_INLIST(&check->buf_wait.list))
                 LIST_DEL_INIT(&check->buf_wait.list);
 
-	task_set_affinity(t, MAX_THREADS_MASK);
+	task_set_affinity(t, all_threads_mask);
 	check_release_buf(check, &check->bi);
 	check_release_buf(check, &check->bo);
 	check->state &= ~(CHK_ST_INPROGRESS|CHK_ST_IN_ALLOC|CHK_ST_OUT_ALLOC);