ehea: propagate physical port state

Introduces a module parameter to decide whether the physical
port link state is propagated to the network stack or not.
It makes sense not to take the physical port state into account
on machines with more logical partitions that communicate
with each other. This is always possible no matter what the physical
port state is. Thus eHEA can be considered as a switch there.

Signed-off-by: Jan-Bernd Themann <themann@de.ibm.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>