When a DISCONTIGMEM memory range is brought online as a NUMA node, it
also needs to have its bet set in N_NORMAL_MEMORY. This is necessary for
generic kernel code that utilizes N_NORMAL_MEMORY as a subset of N_ONLINE
for memory savings.
These types of hacks can hopefully be removed once DISCONTIGMEM is either
removed or abstracted away from CONFIG_NUMA.
Fixes a panic in the slub code which only initializes structures for
N_NORMAL_MEMORY to save memory: