liquidio: support use of ethtool to set link speed of CN23XX-225 cards

Support setting the link speed of CN23XX-225 cards (which can do 25Gbps or
10Gbps) via ethtool_ops.set_link_ksettings.

Also fix the function assigned to ethtool_ops.get_link_ksettings to use the
new link_ksettings api completely (instead of partially via
ethtool_convert_legacy_u32_to_link_mode).

Signed-off-by: Weilin Chang <weilin.chang@cavium.com>
Acked-by: Raghu Vatsavayi <raghu.vatsavayi@cavium.com>
Signed-off-by: Felix Manlunas <felix.manlunas@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>