Add "socket" type to the list of default object types, and by

default attempt to list Biba, LOMAC, and MLS label information
for the socket if they are present.

Obtained from:	TrustedBSD Project
Sponsored by:	DARPA, Network Associates Laboratories

etc/mac.conf

@@ -14,4 +14,5 @@
 default_labels file ?biba,?lomac,?mls,?sebsd
 default_labels ifnet ?biba,?lomac,?mls,?sebsd
 default_labels process ?biba,?lomac,?mls,?partition,?sebsd
+default_labels socket ?biba,?lomac,?mls