ipe: add permissive toggle

IPE, like SELinux, supports a permissive mode. This mode allows policy
authors to test and evaluate IPE policy without it affecting their
programs. When the mode is changed, a 1404 AUDIT_MAC_STATUS will
be reported.

This patch adds the following audit records:

    audit: MAC_STATUS enforcing=0 old_enforcing=1 auid=4294967295
      ses=4294967295 enabled=1 old-enabled=1 lsm=ipe res=1
    audit: MAC_STATUS enforcing=1 old_enforcing=0 auid=4294967295
      ses=4294967295 enabled=1 old-enabled=1 lsm=ipe res=1

The audit record only emit when the value from the user input is
different from the current enforce value.

Signed-off-by: Deven Bowers <deven.desai@linux.microsoft.com>
Signed-off-by: Fan Wu <wufan@linux.microsoft.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>