[VLAN]: Avoid a 4-order allocation.

This patch splits the vlan_group struct into a multi-allocated struct. On
x86_64, the size of the original struct is a little more than 32KB, causing
a 4-order allocation, which is prune to problems caused by buddy-system
external fragmentation conditions.

I couldn't just use vmalloc() because vfree() cannot be called in the
softirq context of the RCU callback.

Signed-off-by: Dan Aloni <da-x@monatomic.org>
Acked-by: Jeff Garzik <jeff@garzik.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/chelsio/cxgb2.c

@@ -889,8 +889,7 @@ static void vlan_rx_kill_vid(struct net_device *dev, unsigned short vid)
 	struct adapter *adapter = dev->priv;
 
 	spin_lock_irq(&adapter->async_lock);
-	if (adapter->vlan_grp)
-		adapter->vlan_grp->vlan_devices[vid] = NULL;
+	vlan_group_set_device(adapter->vlan_grp, vid, NULL);
 	spin_unlock_irq(&adapter->async_lock);
 }
 #endif