Introduce a mac_policy() system call that will provide MAC policies

with a general purpose front end entry point for user applications
to invoke.  The MAC framework will route the system call to the
appropriate policy by name.

Obtained from:	TrustedBSD Project
Sponsored by:	DARPA, NAI Labs

sys/kern/syscalls.master

@@ -565,3 +565,5 @@
 392	STD	BSD	{ int uuidgen(struct uuid *store, int count); }
 393	MSTD	BSD	{ int sendfile(int fd, int s, off_t offset, size_t nbytes, \
 				struct sf_hdtr *hdtr, off_t *sbytes, int flags); }
+394	MNOIMPL	BSD	{ int mac_policy(const char *policy, int call, \
+				void *arg); }