Consistently name functions for mac_<policy> as <policy>_whatever rather

Consistently name functions for mac_<policy> as <policy>_whatever rather
than mac_<policy>_whatever, as this shortens the names and makes the code
a bit easier to read.

When dealing with label structures, name variables 'mb', 'ml', 'mm rather
than the longer 'mac_biba', 'mac_lomac', and 'mac_mls', likewise making
the code a little easier to read.

Obtained from:	TrustedBSD Project