r8169: Use a different default for each family

The r8169 driver supports 3 different families of network chips
(RTL8169, RTL8168 and RTL8101). When an unknown version is found, the
driver currently always defaults to the RTL8169 variant. This has very
little chance to ever work for chips of the other families. So better
define a per-family default.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Acked-by: Francois Romieu <romieu@fr.zoreil.com>
Signed-off-by: David S. Miller <davem@davemloft.net>