audit: convert sessionid unset to a macro

Use a macro, "AUDIT_SID_UNSET", to replace each instance of
initialization and comparison to an audit session ID.

Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
diff --git a/include/linux/audit.h b/include/linux/audit.h
index b639cf1..2d15bce 100644
--- a/include/linux/audit.h
+++ b/include/linux/audit.h
@@ -510,7 +510,7 @@ static inline kuid_t audit_get_loginuid(struct task_struct *tsk)
 }
 static inline unsigned int audit_get_sessionid(struct task_struct *tsk)
 {
-	return -1;
+	return AUDIT_SID_UNSET;
 }
 static inline void audit_ipc_obj(struct kern_ipc_perm *ipcp)
 { }