nit6xlite_defconfig: add CONFIG_SLUB_DEBUG to keep Ubuntu happy

See these pages for reference:
	https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1090308
	http://manpages.ubuntu.com/manpages/saucy/en/man5/slabinfo.5.htm

Signed-off-by: Eric Nelson <eric.nelson@boundarydevices.com>