If mac-address is changed using "setenv ethaddr ...." command the new
mac-adress also must be written into the responsible ethernet driver.
This fixes the legacy ethernet handling.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Hannes Schmelzer <oe5hpm@oevsv.at>
Cc: Joe Hershberger <joe.hershberger@ni.com>
Cc: Tom Rini <trini@konsulko.com>
Reviewed-by: Hannes Schmelzer <oe5hpm@oevsv.at>