[NET] dev_change_name: ignore changes to same name

Prevent error/backtrace from dev_rename() when changing
name of network device to the same name. This is a common
situation with udev and other scripts that bind addr to device.

Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>