net: rename group sysfs entry to netdev_group

commit a512b92b adds sysfs entry for net device group, but
before this commit, tun also uses group sysfs, so after this
commit checkin, kernel warns like this:
    sysfs: cannot create duplicate filename '/devices/virtual/net/vnet0/group'

Since tun has used this for years, rename sysfs under tun might
break existing userspace, so rename group sysfs entry for net device
group is a better choice.
Signed-off-by: NXiaotian Feng <dfeng@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/net-sysfs.c

@@ -330,7 +330,7 @@ static struct device_attribute net_class_attributes[] = {
 	__ATTR(flags, S_IRUGO | S_IWUSR, show_flags, store_flags),
 	__ATTR(tx_queue_len, S_IRUGO | S_IWUSR, show_tx_queue_len,
 	       store_tx_queue_len),
-	__ATTR(group, S_IRUGO | S_IWUSR, show_group, store_group),
+	__ATTR(netdev_group, S_IRUGO | S_IWUSR, show_group, store_group),
 	{}
 };