r8169: MSI support

It is currently limited to the tested 0x8136 and 0x8168. 8169sb/8110sb ought
to handle it as well where they support MSI.

Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Cc: Edward Hsu <edward_hsu@realtek.com.tw>
Tester-Cc: Rolf Eike Beer <eike-kernel@sf-tec.de>