Some RTL8169 cards (observed with an RTL8169SC) power up advertising
only 100Mbps, despite being capable of 1000Mbps. Forcibly enable
advertisement of 1000Mbps on any RTL8169-like card.
This change relies on the assumption that the CTRL1000 register will
not exist on 100Mbps-only RTL8169 cards such as the RTL8101.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
5676abead2