net: make struct net_device::tx_queue_len unsigned int

4 billion packet queue is something unthinkable so use 32-bit value
for now.

Space savings on x86_64:

	add/remove: 0/0 grow/shrink: 3/70 up/down: 16/-131 (-115)
	function                                     old     new   delta
	change_tx_queue_len                           94     108     +14
	qdisc_create                                1176    1177      +1
	alloc_netdev_mqs                            1124    1125      +1
	xenvif_alloc                                 533     532      -1
	x25_asy_setup                                167     166      -1
			...
	tun_queue_resize                             945     940      -5
	pfifo_fast_enqueue                           167     162      -5
	qfq_init_qdisc                               168     158     -10
	tap_queue_resize                             810     799     -11
	transmit                                     719     698     -21

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index 65ea0ff..58e6cc7 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -323,7 +323,11 @@ NETDEVICE_SHOW_RW(flags, fmt_hex);
 
 static int change_tx_queue_len(struct net_device *dev, unsigned long new_len)
 {
-	int res, orig_len = dev->tx_queue_len;
+	unsigned int orig_len = dev->tx_queue_len;
+	int res;
+
+	if (new_len != (unsigned int)new_len)
+		return -ERANGE;
 
 	if (new_len != orig_len) {
 		dev->tx_queue_len = new_len;
@@ -349,7 +353,7 @@ static ssize_t tx_queue_len_store(struct device *dev,
 
 	return netdev_store(dev, attr, buf, len, change_tx_queue_len);
 }
-NETDEVICE_SHOW_RW(tx_queue_len, fmt_ulong);
+NETDEVICE_SHOW_RW(tx_queue_len, fmt_dec);
 
 static int change_gro_flush_timeout(struct net_device *dev, unsigned long val)
 {