ehea: set mac address fix

eHEA has to call firmware functions in order to change the mac address
of a logical port. This patch checks if the logical port is up
when calling the register / deregister mac address calls. If the port
is down these firmware calls would fail and are therefore not executed.

Signed-off-by: Jan-Bernd Themann <themann@de.ibm.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>