audit: prepare audit_context for use in calling contexts beyond syscalls

This patch cleans up some of our audit_context handling by
abstracting out the reset and return code fixup handling to dedicated
functions.  Not only does this help make things easier to read and
inspect, it allows for easier reuse by future patches.  We also
convert the simple audit_context->in_syscall flag into an enum which
can be used to by future patches to indicate a calling context other
than the syscall context.

Thanks to Richard Guy Briggs for review and feedback.
Acked-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

kernel/audit.h

@@ -100,7 +100,10 @@ struct audit_proctitle {
 /* The per-task audit context. */
 struct audit_context {
 	int		    dummy;	/* must be the first element */
-	int		    in_syscall;	/* 1 if task is in a syscall */
+	enum {
+		AUDIT_CTX_UNUSED,	/* audit_context is currently unused */
+		AUDIT_CTX_SYSCALL,	/* in use by syscall */
+	} context;
 	enum audit_state    state, current_state;
 	unsigned int	    serial;     /* serial number for record */
 	int		    major;      /* syscall number */