ceph: preserve seq # on requeued messages after transient transport errors

If the tcp connection drops and we reconnect to reestablish a stateful
session (with the mds), we need to resend previously sent (and possibly
received) messages with the _same_ seq # so that they can be dropped on
the other end if needed.  Only assign a new seq once after the message is
queued.

Signed-off-by: Sage Weil <sage@newdream.net>
diff --git a/fs/ceph/messenger.h b/fs/ceph/messenger.h
index a343dae..a5caf91 100644
--- a/fs/ceph/messenger.h
+++ b/fs/ceph/messenger.h
@@ -86,6 +86,7 @@
 	struct kref kref;
 	bool front_is_vmalloc;
 	bool more_to_follow;
+	bool needs_out_seq;
 	int front_max;
 
 	struct ceph_msgpool *pool;