config: switch to SLUB memory allocator

Switch to SLUB instead of SLAB. There are plenty
of reasons for this (performance, stability).
But since our new Wifi driver is linked to the
memory allocator its a nice addition to switch
to a faster one.

Change-Id: I44db4b7504a57b64636db8e07fbc42228df90672
Signed-off-by: Blechd0se <alex.christ@hotmail.de>