[TUN]: Fix RTNL-locking in tun/tap driver

Current tun/tap driver sets also net device's hw address when asked to
change character device's hw address. This is a good idea, but it
misses RTLN-locking, resulting following error message in 2.6.25-rc3's
inetdev_event() function:

RTNL: assertion failed at net/ipv4/devinet.c (1050)

Attached patch fixes this problem.
Signed-off-by: NKim B. Heino <Kim.Heino@bluegiga.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/tun.c

@@ -663,7 +663,11 @@ static int tun_chr_ioctl(struct inode *inode, struct file *file,
 	case SIOCSIFHWADDR:
 	{
 		/* try to set the actual net device's hw address */
-		int ret = dev_set_mac_address(tun->dev, &ifr.ifr_hwaddr);
+		int ret;
+
+		rtnl_lock();
+		ret = dev_set_mac_address(tun->dev, &ifr.ifr_hwaddr);
+		rtnl_unlock();
 
 		if (ret == 0) {
 			/** Set the character device's hardware address. This is used when