r8169: get ethtool settings through the generic mii helper

It avoids to report unsupported link capabilities with
the fast-ethernet only 8101/8102.

Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Tested-by: Martin Capitanio <martin@capitanio.org>
Fixed-by: Ivan Vecera <ivecera@redhat.com>
Cc: Edward Hsu <edward_hsu@realtek.com.tw>