us to reduce namespace pollution by doing a nested include of _label.h
rather than mac.h. mac.h contains lots of baggage, whereas _label.h
contains much less. A follow-up sweep to change nested inclusion will
follow. The problem regarding exporting 'struct label' to userland
due to excessive exporting of kernel structures to userland still
needs to be resolved.
Obtained from: TrustedBSD Project
Sponsored by: DARPA, NAI Labs
Suggested by: bde
de88edcff7