net: create sysfs symlinks for neighbour devices

net: create sysfs symlinks for neighbour devices

Also, remove the same functionality from bonding - it will be already done
for any device that links to its lower/upper neighbour.

The links will be created for dev's kobject, and will look like
lower_eth0 for lower device eth0 and upper_bridge0 for upper device
bridge0.

CC: Jay Vosburgh <[email protected]>
CC: Andy Gospodarek <[email protected]>
CC: "David S. Miller" <[email protected]>
CC: Eric Dumazet <[email protected]>
CC: Jiri Pirko <[email protected]>
CC: Alexander Duyck <[email protected]>
Signed-off-by: Veaceslav Falico <[email protected]>
Signed-off-by: David S. Miller <[email protected]>