AUDIT: Prevent duplicate syscall rules

The following patch against audit.81 prevents duplicate syscall rules in
a given filter list by walking the list on each rule add.

I also removed the unused struct audit_entry in audit.c and made the
static inlines in auditsc.c consistent.

Signed-off-by: Amy Griffis <amy.griffis@hp.com>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>