Add UNPLUG traces to all appropriate places

Added blk_unplug interface, allowing all invocations of unplugs to result
in a generated blktrace UNPLUG.

Signed-off-by: Alan D. Brunelle <Alan.Brunelle@hp.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 808cd95..cef9ebd 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -5445,7 +5445,7 @@
 		 * about not overloading the IO subsystem. (things like an
 		 * e2fsck being done on the RAID array should execute fast)
 		 */
-		mddev->queue->unplug_fn(mddev->queue);
+		blk_unplug(mddev->queue);
 		cond_resched();
 
 		currspeed = ((unsigned long)(io_sectors-mddev->resync_mark_cnt))/2
@@ -5464,7 +5464,7 @@
 	 * this also signals 'finished resyncing' to md_stop
 	 */
  out:
-	mddev->queue->unplug_fn(mddev->queue);
+	blk_unplug(mddev->queue);
 
 	wait_event(mddev->recovery_wait, !atomic_read(&mddev->recovery_active));