[IrDA]: irda-usb TX path optimization (was Re: IrDA spams logfiles - since 2.6.19)

Since we stop using dev_alloc_skb on the IrDA TX frame, we constantly run
into the case of the skb headroom being 0, and thus we call skb_cow for
every IrDA TX frame.
This patch uses a local buffer and memcpy the skb to it, saving us a
kmalloc for each of those IrDA TX frames.

Signed-off-by: Samuel Ortiz <samuel@sortiz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/irda/irda-usb.h b/drivers/net/irda/irda-usb.h
index 6b2271f..e846c38 100644
--- a/drivers/net/irda/irda-usb.h
+++ b/drivers/net/irda/irda-usb.h
@@ -156,6 +156,7 @@
 	struct irlap_cb   *irlap;	/* The link layer we are binded to */
 	struct qos_info qos;
 	char *speed_buff;		/* Buffer for speed changes */
+	char *tx_buff;
 
 	struct timeval stamp;
 	struct timeval now;