drbd: drbd_send(): Return a "real" error code if we have no socket

Q: Can this case even trigger?  Is failing this way any better than one
that causes a NULL pointer access?

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

drivers/block/drbd/drbd_main.c

@@ -1703,7 +1703,7 @@ int drbd_send(struct drbd_tconn *tconn, struct socket *sock,
 	int rv, sent = 0;
 
 	if (!sock)
-		return -1000;
+		return -EBADR;
 
 	/* THINK  if (signal_pending) return ... ? */