x86_64: add kmod-r8169 to the default packages

This kmod is required by the Alix APU 1D4 to be reachable after
installing an x86-64 image.

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@42945 3c298f89-4303-0410-b956-a3cf2f4a3e73