vlan: propogate ethtool speed values

This enables more ethtool information. The speed and settings of the
underlying device are propagated up. This makes services like SNMP that
use ethtool to get speed setting, work when managing a vlan, without adding
silly heurtistics into SNMP daemon.

For the driver info, just use existing driver strings.

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