ceph: include transaction id in ceph_msg_header (protocol change)

Many (most?) message types include a transaction id.  By including it in
the fixed size header, we always have it available even when we are unable
to allocate memory for the (larger, variable sized) message body.  This
will allow us to error out the appropriate request instead of (silently)
dropping the reply.

Signed-off-by: Sage Weil <sage@newdream.net>
diff --git a/fs/ceph/msgr.h b/fs/ceph/msgr.h
index c758e8f..e46d8b8 100644
--- a/fs/ceph/msgr.h
+++ b/fs/ceph/msgr.h
@@ -21,7 +21,7 @@
  * whenever the wire protocol changes.  try to keep this string length
  * constant.
  */
-#define CEPH_BANNER "ceph v024"
+#define CEPH_BANNER "ceph v025"
 #define CEPH_BANNER_MAX_LEN 30
 
 
@@ -132,6 +132,7 @@
  */
 struct ceph_msg_header {
 	__le64 seq;       /* message seq# for this session */
+	__le64 tid;       /* transaction id */
 	__le16 type;      /* message type */
 	__le16 priority;  /* priority.  higher value == higher priority */
 	__le16 version;   /* version of message encoding */