firewire: cdev: extend transaction payload size check

Make the size check of ioctl_send_request and
ioctl_send_broadcast_request speed dependent.  Also change the error
return code from -EINVAL to -EIO to distinguish this from other errors
concerning the ioctl parameters.

Another payload size limit for which we don't check here though is the
remote node's Bus_Info_Block.max_rec.
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>

drivers/firewire/fw-cdev.c

@@ -525,9 +525,8 @@ static int init_request(struct client *client,
 	struct outbound_transaction_event *e;
 	int ret;
 
-	/* What is the biggest size we'll accept, really? */
-	if (request->length > 4096)
-		return -EINVAL;
+	if (request->length > 4096 || request->length > 512 << speed)
+		return -EIO;
 
 	e = kmalloc(sizeof(*e) + request->length, GFP_KERNEL);
 	if (e == NULL)