net: thunderx: Switchon carrier only upon interface link up

Call netif_carrier_on() only if interface's link is up. Switching this on
upon IFF_UP by default, is causing issues with ethernet channel bonding
in LACP mode. Initial NETDEV_CHANGE notification was being skipped.

Also fixed some issues with link/speed/duplex reporting via ethtool.

Signed-off-by: Sunil Goutham <sgoutham@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>