Fix the same bug when getting a slab's name in ksalloc
Fix the same bug when getting a slab's name in ksalloc

Previously, we always used the name of CPU 0's kmem for a slab (owing
to the same type of pointer decay problem fixed by the last commit).
This is why all mtrace labels are called things like "0kstack" instead
of having the right CPU number.

aclements/sv6,aclements/sv6,aclements/sv6,aclements/sv6,bowlofstew/sv6,bowlofstew/sv6,bowlofstew/sv6,aclements/sv6,bowlofstew/sv6,bowlofstew/sv6