libceph: initialize ack_stamp to avoid unnecessary connection reset

Commit 4cf9d544 recorded when an outgoing ceph message was ACKed,
in order to avoid unnecessary connection resets when an OSD is busy.

However, ack_stamp is uninitialized, so there is a window between
when the message is sent and when it is ACKed in which handle_timeout()
interprets the unitialized value as an expired timeout, and resets
the connection unnecessarily.

Close the window by initializing ack_stamp.
Signed-off-by: Jim Schutt <jaschut@sandia.gov>
Signed-off-by: Sage Weil <sage@newdream.net>

net/ceph/messenger.c

@@ -2307,6 +2307,7 @@ struct ceph_msg *ceph_msg_new(int type, int front_len, gfp_t flags)
 	m->front_max = front_len;
 	m->front_is_vmalloc = false;
 	m->more_to_follow = false;
+	m->ack_stamp = 0;
 	m->pool = NULL;
 
 	/* middle */