cdc_ether: Partially revert "usbnet: Set link down initially ..."

Commit 37e8273c ("usbnet: Set link down
initially for drivers that update link state") changed the initial link
state in cdc_ether and other drivers based on the understanding that the
devices they support generate link change interrupts.  However, this is
optional in the CDC Ethernet protocol, and two users have reported in
<http://bugzilla.kernel.org/show_bug.cgi?id=14791

> that the link state
for their devices remains down.  Therefore, revert the change in
cdc_ether.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Tested-by: Avi Rozen <avi.rozen@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>