irda: Add irda_skb_cb qdisc related padding

We need to pad irda_skb_cb in order to keep it safe accross dev_queue_xmit()
calls. This is some ugly and temporary hack triggered by recent qisc code
changes.
Even though it fixes bugzilla.kernel.org bug #11795, it will be replaced by a
proper fix before 2.6.29 is released.

Signed-off-by: Samuel Ortiz <samuel@sortiz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>