net: rename group sysfs entry to netdev_group

commit a512b92 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: Xiaotian Feng <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/core/net-sysfs.c

···
 	__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),
 	{}
 };