[WAN] hdlc_cisco: Fix regression introduced by skb->tail changes.

The following commit breaks cisco mode with my WAN drivers:
author David S. Miller <[e-mail]>
Tue, 28 Jun 2005 22:25:31 +0000 (15:25 -0700)
commit 689be43945e9ca7dd704522e55af1b8a73a994d3

"[NET]: Remove gratuitous use of skb->tail in network drivers."

The following patch fixes it - please apply (cisco_hard_header does
skb_push(4 bytes)).

Signed-off-by: David S. Miller <[e-mail]>

drivers/net/wan/hdlc_cisco.c

···
 	}
 	skb_reserve(skb, 4);
 	cisco_hard_header(skb, dev, CISCO_KEEPALIVE, NULL, NULL, 0);
-	data = (cisco_packet*)skb->data;
+	data = (cisco_packet*)(skb->data + 4);
 
 	data->type = htonl(type);
 	data->par1 = htonl(par1);