ocfs2: Add some trace log for orphan scan.

Now orphan scan worker has no trace log, so it is
very hard to tell whether it is finished or blocked.
So add 2 mlog trace log so that we can tell whether
the current orphan scan worker is blocked or not.
It does help when I analyzed a orphan scan bug.
Signed-off-by: NTao Ma <tao.ma@oracle.com>
Signed-off-by: NJoel Becker <joel.becker@oracle.com>

fs/ocfs2/journal.c

@@ -1888,6 +1888,8 @@ void ocfs2_queue_orphan_scan(struct ocfs2_super *osb)
 
 	os = &osb->osb_orphan_scan;
 
+	mlog(0, "Begin orphan scan\n");
+
 	if (atomic_read(&os->os_state) == ORPHAN_SCAN_INACTIVE)
 		goto out;
 
@@ -1920,6 +1922,7 @@ void ocfs2_queue_orphan_scan(struct ocfs2_super *osb)
 unlock:
 	ocfs2_orphan_scan_unlock(osb, seqno);
 out:
+	mlog(0, "Orphan scan completed\n");
 	return;
 }