drbd: Fix disconnect to keep the peer disk state if connection breaks during operation

The issue was that if the connection broke while we did the
gracefull state change to C_DISCONNECTING (C_TEARDOWN), then
we returned a success code from the state engine. (SS_CW_NO_NEED)

The result of that is that we missed to call the fence-peer
script in such a case.

Fixed that by introducing a new error code (SS_OUTDATE_WO_CONN).
This one should never reach back into user space.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/include/linux/drbd.h b/include/linux/drbd.h
index 0c5a18e..3163307 100644
--- a/include/linux/drbd.h
+++ b/include/linux/drbd.h
@@ -319,7 +319,8 @@
 	SS_IN_TRANSIENT_STATE = -18,  /* Retry after the next state change */
 	SS_CONCURRENT_ST_CHG = -19,   /* Concurrent cluster side state change! */
 	SS_O_VOL_PEER_PRI = -20,
-	SS_AFTER_LAST_ERROR = -21,    /* Keep this at bottom */
+	SS_OUTDATE_WO_CONN = -21,
+	SS_AFTER_LAST_ERROR = -22,    /* Keep this at bottom */
 };
 
 /* from drbd_strings.c */