r8169: more alignment for the 0x8168

Two thirds of packets are lost because of misalignment. Users of
Asus laptop did apparently not notice it.

Reported on Gigabyte GA-945GM-S2.

Fix for http://bugzilla.kernel.org/show_bug.cgi?id=7517



Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>