dm raid1: wake kmirrord when requeueing delayed bios after remote recovery

The recent commit 7513c2a7 (dm raid1:
add is_remote_recovering hook for clusters) changed do_writes() to
update the ms->writes list but forgot to wake up kmirrord to process it.

The rule is that when anything is being added on ms->reads, ms->writes
or ms->failures and the list was empty before we must call
wakeup_mirrord (for immediate processing) or delayed_wake (for delayed
processing).  Otherwise the bios could sit on the list indefinitely.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
CC: stable@kernel.org
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

drivers/md/dm-raid1.c

@@ -638,6 +638,7 @@ static void do_writes(struct mirror_set *ms, struct bio_list *writes)
 		spin_lock_irq(&ms->lock);
 		bio_list_merge(&ms->writes, &requeue);
 		spin_unlock_irq(&ms->lock);
+		delayed_wake(ms);
 	}
 
 	/*