audit: make ANOM_LINK obey audit_enabled and audit_dummy_context

Audit link denied events emit disjointed records when audit is disabled.
No records should be emitted when audit is disabled.

See: https://github.com/linux-audit/audit-kernel/issues/21



Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>