netdev: use const for some name functions

dev_change_name and netdev_drivername should use const char on
parameters that are read-only input values. The strcpy to newname is
not needed since newname is not used later in function.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>