oxnas: refresh kernel config-3.1[48]

and no longer compile-in ext4 filesystem now that sata_oxnas is
also built as a module.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@43765 3c298f89-4303-0410-b956-a3cf2f4a3e73