[NET]: Fix loopback crashes when multiqueue is enabled.

From: Patrick McHardy <kaber@trash.net>

Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -575,7 +575,7 @@ struct net_device
 
 	/* The TX queue control structures */
 	unsigned int			egress_subqueue_count;
-	struct net_device_subqueue	egress_subqueue[0];
+	struct net_device_subqueue	egress_subqueue[1];
 };
 #define to_net_dev(d) container_of(d, struct net_device, dev)
 

net/core/dev.c

@@ -3624,7 +3624,7 @@ struct net_device *alloc_netdev_mq(int sizeof_priv, const char *name,
 
 	/* ensure 32-byte alignment of both the device and private area */
 	alloc_size = (sizeof(*dev) + NETDEV_ALIGN_CONST +
-		     (sizeof(struct net_device_subqueue) * queue_count)) &
+		     (sizeof(struct net_device_subqueue) * (queue_count - 1))) &
 		     ~NETDEV_ALIGN_CONST;
 	alloc_size += sizeof_priv + NETDEV_ALIGN_CONST;
 
@@ -3642,7 +3642,7 @@ struct net_device *alloc_netdev_mq(int sizeof_priv, const char *name,
 		dev->priv = ((char *)dev +
 			     ((sizeof(struct net_device) +
 			       (sizeof(struct net_device_subqueue) *
-				queue_count) + NETDEV_ALIGN_CONST)
+				(queue_count - 1)) + NETDEV_ALIGN_CONST)
 			      & ~NETDEV_ALIGN_CONST));
 	}