This will prevent dropping packets from domU to vif in dom0.

Idea from: Dominique Rousseau <d.rousseau@xxxxxxx>
Patch by: Daniele Palumbo <daniele@xxxxxxxxxxxx>

diff -Nur drivers/xen/netback.orig/common.h drivers/xen/netback/common.h
--- drivers/xen/netback.orig/common.h	2006-09-14 15:52:10.000000000 +0200
+++ drivers/xen/netback/common.h	2006-09-14 15:52:18.000000000 +0200
@@ -38,6 +38,7 @@
 #include <linux/in.h>
 #include <linux/netdevice.h>
 #include <linux/etherdevice.h>
+#include <linux/if_vlan.h>
 #include <xen/evtchn.h>
 #include <xen/interface/io/netif.h>
 #include <asm/io.h>
diff -Nur drivers/xen/netback.orig/netback.c drivers/xen/netback/netback.c
--- drivers/xen/netback.orig/netback.c	2006-09-14 10:09:10.000000000 +0200
+++ drivers/xen/netback/netback.c	2006-09-14 15:49:30.000000000 +0200
@@ -548,8 +548,12 @@
 
 		netif_schedule_work(netif);
 
+		/* Accept packet for vlan.
+		 * linux-src/include/linux/if_vlan.h:#define VLAN_ETH_FRAME_LEN    1518
+		 * linux-src/include/linux/if_ether.h:#define ETH_FRAME_LEN        1514
+		 */
 		if (unlikely(txreq.size < ETH_HLEN) || 
-		    unlikely(txreq.size > ETH_FRAME_LEN)) {
+		    unlikely(txreq.size > VLAN_ETH_FRAME_LEN)) {
 			DPRINTK("Bad packet size: %d\n", txreq.size);
 			make_tx_response(netif, txreq.id, NETIF_RSP_ERROR);
 			netif_put(netif);